Process for promoting catalyst activity for ethyl acetate conversion

ABSTRACT

The process of the current invention relates to the production of ethanol from a crude ethanol product obtained from the hydrogenation of acetic acid and ethyl acetate in the presence of a catalyst. Conversion of ethyl acetate may be improved by adding water to the reactor. At least 0.01 wt. % water may be added to the reactor. The crude ethanol product is separated in one or more columns to yield an ethanol product.

CROSS REFERENCE TO RELATED APPLICATION

This application claims priority to U.S. Provisional App. No.61/581,274, filed on Dec. 29, 2011, the entire contents and disclosuresof which are incorporated herein by reference.

FIELD OF THE INVENTION

The present invention relates generally to processes for recoveringethanol produced by the hydrogenation of acetic acid, ethyl acetate, andmixtures thereof in the presence of a catalyst. In particular, thepresent invention relates to feeding at least 0.01 wt. % water topromote catalyst activity for ethyl acetate conversion.

BACKGROUND OF THE INVENTION

Ethanol for industrial use is conventionally produced from organic feedstocks, such as petroleum oil, natural gas, or coal, from feed stockintermediates, such as syngas, or from starchy materials or cellulosicmaterials, such as corn or sugar cane. Conventional methods forproducing ethanol from organic feed stocks, as well as from cellulosicmaterials, include the acid-catalyzed hydration of ethylene, methanolhomologation, direct alcohol synthesis, and Fischer-Tropsch synthesis.Instability in organic feed stock prices contributes to fluctuations inthe cost of conventionally produced ethanol, making the need foralternative sources of ethanol production all the greater when feedstock prices rise. Starchy materials, as well as cellulosic materials,are converted to ethanol by fermentation. However, fermentation istypically used for consumer production of ethanol, which is suitable forfuels or human consumption. In addition, fermentation of starchy orcellulosic materials competes with food sources and places restraints onthe amount of ethanol that can be produced for industrial use.

Ethanol production via the reduction of alkanoic acids and/or othercarbonyl group-containing compounds has been widely studied, and avariety of combinations of catalysts, supports, and operating conditionshave been mentioned in the literature. During the reduction of alkanoicacid, e.g., acetic acid, other compounds are formed with ethanol or areformed in side reactions. These impurities limit the production andrecovery of ethanol from such reaction mixtures. For example, duringhydrogenation, esters are produced that together with ethanol and/orwater form azeotropes, which are difficult to separate. In addition whenconversion is incomplete, unreacted acid remains in the crude ethanolproduct, which must be removed to recover ethanol.

EP02060553 describes a process for converting hydrocarbons to ethanolinvolving converting the hydrocarbons to ethanoic acid and hydrogenatingthe ethanoic acid to ethanol. The stream from the hydrogenation reactoris separated to obtain an ethanol product and a stream of acetic acidand ethyl acetate, which is recycled to the hydrogenation reactor.

U.S. Pat. No. 7,842,844 describes a process for improving selectivityand catalyst activity and operating life for the conversion ofhydrocarbons to ethanol and optionally acetic acid in the presence of aparticulate catalyst, said conversion proceeding via a syngas generationintermediate step.

US Pub. No. 2011/0224462 a process for producing methanol and ethanol,wherein the methanol is produced from synthesis gas and the ethanol isproduced via the hydrogenation of an ethanoic acid feed. Thehydrogenation of the ethanoic acid feed is carried out within the samealcohol synthesis unit and in the presence of the same catalyst(s) thatis used to produce the methanol from the synthesis gas and wherein thefeed introduced to the alcohol synthesis unit comprises synthesis gasand ethanoic acid. The ethanoic acid feed may contain water in an amountbetween 0.5 and 20 mol %.

The need remains for improved processes for recovering ethanol from acrude product obtained by reducing alkanoic acids, such as acetic acid,and/or other carbonyl group-containing compounds.

SUMMARY OF THE INVENTION

In a first embodiment, the present invention is directed to a processfor a process for producing ethanol, comprising hydrogenating a feedstream in a reactor in the presence of a catalyst to form a crudeethanol product, separating at least a portion of the crude ethanolproduct in two or more columns to produce ethanol and a liquid recyclestream comprising ethyl acetate, wherein the feed stream is produced bycombining an acetic acid stream and the liquid recycle stream,determining ethyl acetate concentration in the crude ethanol product,and adding at least 0.01 wt. % water, e.g., at least 0.1 wt. %, at least1 wt. %, to the feed stream for maintaining an ethyl acetate conversionof greater than 0%, when the ethyl acetate concentration of the crudeethanol product is greater than the ethyl acetate concentration of thefeed stream. When ethyl acetate conversion is negative, at least 0.01wt. % water, e.g., at least 0.1 wt. % or at least 1 wt. %, may be addedto the vaporizer. In some embodiments, from 0.01 to 20 wt. % water isadded to the vaporizer when ethyl acetate conversion is negative. Theliquid recycle stream preferably comprises ethyl acetate and issubstantially free of acetic acid. The liquid recycle stream may alsocomprise mixtures of acetaldehyde, diethyl acetal, ethanol, and/orwater. The volumetric ratio of acetic acid stream to liquid recyclestream may be at least 1.5:1 and may range from 1.5:1 to 20:1, e.g.,from 1.5:1 to 5:1. The conversion of ethyl acetate after adding water tothe vaporizer may be at least 1% or at least 3%. In some embodiments,the conversion of ethyl acetate is at least 15%. In some embodiments,the catalyst comprises a first metal selected from the group consistingof iron, cobalt, nickel, ruthenium, rhodium, palladium, osmium, iridium,platinum, titanium, chromium, rhenium, molybdenum, and tungsten, and asecond metal is selected from the group consisting of molybdenum, tin,chromium, iron, cobalt, vanadium, tungsten, palladium, platinum,lanthanum, cerium, manganese, ruthenium, rhenium, gold, and nickel,wherein the second metal is different than the first metal. In otherembodiments, the catalyst is substantially free of copper, zinc, andoxides thereof. The acetic acid may be formed from methanol and carbonmonoxide, wherein each of the methanol, the carbon monoxide, andhydrogen for the hydrogenating step is derived from syngas, and whereinthe syngas is derived from a carbon source selected from the groupconsisting of natural gas, oil, petroleum, coal, biomass, andcombinations thereof.

In a second embodiment, the present invention is directed to a processfor producing ethanol, comprising: hydrogenating a feed stream in areactor in the presence of a catalyst to form a crude ethanol product;separating at least a portion of the crude ethanol product in a firstdistillation column to yield a first residue comprising acetic acid anda first distillate comprising ethanol, ethyl acetate, and water;removing water from at least a portion of the first distillate to yieldan ethanol mixture stream comprising less than 10 wt. % water;separating a portion of the ethanol mixture stream in a seconddistillation column to yield a second residue comprising ethanol and asecond distillate comprising ethyl acetate, wherein the feed stream isproduced by combining an acetic acid stream and a liquid recycle stream;determining ethyl acetate concentration in the crude ethanol product;and adding at least 0.01 wt. % water to the feed stream for maintainingan ethyl acetate conversion of greater than 0%, when the ethyl acetateconcentration of the crude ethanol product is greater than the ethylacetate concentration of the feed stream. When ethyl acetate conversionis negative, at least 0.01 wt. % water, e.g., at least 0.1 wt. % or atleast 1 wt. %, may be added to the vaporizer. In some embodiments, from0.01 to 20 wt. % water is added to the vaporizer when ethyl acetateconversion is negative. In some embodiments, the catalyst comprises afirst metal selected from the group consisting of iron, cobalt, nickel,ruthenium, rhodium, palladium, osmium, iridium, platinum, titanium,chromium, rhenium, molybdenum, and tungsten, and a second metal isselected from the group consisting of molybdenum, tin, chromium, iron,cobalt, vanadium, tungsten, palladium, platinum, lanthanum, cerium,manganese, ruthenium, rhenium, gold, and nickel, wherein the secondmetal is different than the first metal. In other embodiments, thecatalyst is substantially free of copper, zinc, and oxides thereof.

In a third embodiment, the present invention is directed to a processfor producing ethanol, comprising: hydrogenating a feed stream in areactor in the presence of a catalyst to form a crude ethanol product;separating a portion of the crude ethanol product in a firstdistillation column to yield a first distillate comprising ethyl acetateand acetaldehyde, and a first residue comprising ethanol, acetic acid,water or mixtures thereof; separating a portion of the first residue ina second distillation column to yield a second residue comprising aceticacid and water and a second distillate comprising ethanol and ethylacetate; separating a portion of the second distillate in a thirddistillation column to yield a third residue comprising ethanol and athird distillate comprising ethyl acetate, wherein the feed stream isproduced by combining an acetic acid stream and a liquid recycle stream;determining ethyl acetate concentration in the crude ethanol product;and adding at least 0.01 wt. % water to the feed stream for maintainingan ethyl acetate conversion of greater than 0%, when the ethyl acetateconcentration of the crude ethanol product is greater than the ethylacetate concentration of the feed stream. When ethyl acetate conversionis negative, at least 0.01 wt. % water, e.g., at least 0.1 wt. % or atleast 1 wt. %, may be added to the vaporizer. In some embodiments, from0.01 to 20 wt. % water is added to the vaporizer when ethyl acetateconversion is negative. In some embodiments, the catalyst comprises afirst metal selected from the group consisting of iron, cobalt, nickel,ruthenium, rhodium, palladium, osmium, iridium, platinum, titanium,chromium, rhenium, molybdenum, and tungsten, and a second metal isselected from the group consisting of molybdenum, tin, chromium, iron,cobalt, vanadium, tungsten, palladium, platinum, lanthanum, cerium,manganese, ruthenium, rhenium, gold, and nickel, wherein the secondmetal is different than the first metal. In other embodiments, thecatalyst is substantially free of copper, zinc, and oxides thereof.

In a fourth embodiment, the present invention is directed to a processfor producing ethanol, comprising providing a crude ethanol product;separating at least a portion of the crude ethanol product in two ormore columns to produce ethanol and a liquid recycle stream comprisingethyl acetate, wherein the feed stream is produced by combining anacetic acid stream and a liquid recycle stream; determining ethylacetate concentration in the crude ethanol product; and adding at least0.01 wt. % water to the feed stream for maintaining an ethyl acetateconversion of greater than 0%, when the ethyl acetate concentration ofthe crude ethanol product is greater than the ethyl acetateconcentration of the feed stream. When ethyl acetate conversion isnegative, at least 0.01 wt. % water, at least 0.1 wt. % or at least 1wt. %, may be added to the vaporizer. In some embodiments, from 0.01 to20 wt. % water is added to the vaporizer when ethyl acetate conversionis negative. In some embodiments, the catalyst comprises a first metalselected from the group consisting of iron, cobalt, nickel, ruthenium,rhodium, palladium, osmium, iridium, platinum, titanium, chromium,rhenium, molybdenum, and tungsten, and a second metal is selected fromthe group consisting of molybdenum, tin, chromium, iron, cobalt,vanadium, tungsten, palladium, platinum, lanthanum, cerium, manganese,ruthenium, rhenium, gold, and nickel, wherein the second metal isdifferent than the first metal. In other embodiments, the catalyst issubstantially free of copper, zinc, and oxides thereof.

In a fifth embodiment, the present invention is directed to a processfor producing ethanol, comprising: hydrogenating a feed stream in areactor in the presence of a catalyst to form a crude ethanol product;separating at least a portion of the crude ethanol product in two ormore columns to produce ethanol and a liquid recycle stream comprisingethyl acetate, wherein the feed stream is produced by combining anacetic acid stream and a liquid recycle stream; and maintaining a waterconcentration in the feed stream and maintaining a constant ethylacetate concentration in the reactor; provided that when the ethylacetate conversion is less than 0%, the process further comprises addingexcess water to the feed stream to maintain the constant ethyl acetateconcentration.

BRIEF DESCRIPTION OF DRAWINGS

The invention is described in detail below with reference to theappended drawings, wherein like numerals designate similar parts.

FIG. 1 is a schematic diagram of a hydrogenation process in accordancewith an embodiment of the present invention.

FIG. 2 is a schematic diagram of another hydrogenation process inaccordance with an embodiment of the present invention.

FIG. 3 is a schematic diagram of yet another hydrogenation process inaccordance with an embodiment of the present invention.

DETAILED DESCRIPTION OF THE INVENTION Introduction

The present invention relates to processes for producing ethanol byvaporizing acetic acid and ethyl acetate in a vaporizer to form a feedstream and hydrogenating the feed stream in a reactor in the presence ofa catalyst. The feed stream may comprise acetic acid and ethyl acetate.The catalyst may be a bifunctional catalyst that is capable ofconverting at least some of the acetic acid and ethyl acetate. Thisallows ethyl acetate produced from the hydrogenation of acetic acid tobe recycled and converted without needing to separately purge the ethylacetate.

The hydrogenation reaction produces a crude ethanol product, dependingon acetic acid conversion, that may comprise ethanol, water, ethylacetate, acetaldehyde, acetic acid, or other impurities. The processesof the present invention further comprise separating the crude ethanolproduct to recover ethanol. In some embodiments, at least twodistillation columns are used to separate the crude product. Distillatestreams comprising ethyl acetate and acetaldehyde may be recycled to thevaporizer as liquid recycle streams to reduce the amount of purges. Theliquid recycle stream preferably comprises ethyl acetate and issubstantially free of acetic acid. The liquid recycle stream may alsocomprise mixtures of acetaldehyde, diethyl acetal, ethanol and/or water.The liquid recycle stream is combined with a fresh acetic acid stream,i.e. an acetic acid stream that has not been passed over a catalyst, andboth the liquid recycle stream and acetic acid reactants are vaporizedin the presence of hydrogen to yield a feed stream comprising vaporphase reactants.

Over continuous on stream use, the catalyst activity may decreaserequiring the catalyst to be regenerated or replenished. In a continuousindustrial operation, the facility may require a shutdown toregeneration or replenish the catalyst. Without being bound by theory,the catalyst activity may diminish for ethyl acetate to a greater extentthan for acetic acid. Thus, catalyst activity may be improved bypromoting ethyl acetate conversion. To avoid a loss of catalystactivity, the present invention uses a minor amount of water, in anamount of greater than 0.01 wt. %, to promote the conversion of ethylacetate. The additional water in the feed may promote conversion ofethyl acetate without negatively impacting the conversion of aceticacid. Thus, the catalyst activity may be improved without regeneratingor replenishing the catalyst.

To determine that there is a decrease in ethyl acetate conversion, theethyl acetate concentration of the total feeds to the reactor ismeasured and compared to the crude ethanol product exiting the reactor.When the ethyl acetate concentration of the crude ethanol productexceeds the concentration of ethyl acetate in the total feed(s) to thereactor, there may be catalyst deactivation or a loss of ethyl acetateconversion. Adding water to the feed stream preferably promotes theethyl acetate conversion such that the ethyl acetate concentration ofthe crude ethanol product is lower than the concentration of ethylacetate in the total feed(s) to the reactor. In one embodiment, oncewater is added, the conversion of ethyl acetate is at least 0% or atleast 1%, thus indicating a net consumption of ethyl acetate in thereactor. More preferably, ethyl acetate conversion after adding water isat least 3% or at least 15%.

Because ethyl acetate is recycled to the vaporizer and the hydrogenationreactor, it is important that the catalyst activity is maintained toconvert ethyl acetate. Without converting ethyl acetate, there may be anet increase in ethyl acetate. For purposes of the present invention,this net increase in ethyl acetate may be referred to as a conversion ofethyl acetate of less than 0% or as a negative conversion. One drawbackto ethyl acetate formation is that ethyl acetate may build up in thereactor, leading to reduced ethanol production.

In one embodiment, water is fed to the reactor and preferably to thevaporizer that converts acetic acid to a vapor feed stream. Water may befed separately to the vaporizer as a water stream or may be combinedwith the acetic acid stream and liquid recycle streams and then fed tothe vaporizer. Preferably water is from a liquid recycle stream obtainedby separating the crude ethanol product and is fed to the vaporizer. Thepresent of water in the liquid recycle stream does not substantiallyimpact the reactor and may improve the performance of the catalyst, inparticular for mixtures of acetic acid and ethyl acetate. This mayreduce the energy required to purify the recycle streams because it isnot necessary to completely dry the recycle stream before returning themto the reactor. Water may also be fed to the vaporizer from an externalsource, such as contained in the acetic acid feed source as described inUS Pub. Nos. 2012/0059197 or 2012/0010439, the entire contents anddisclosures of which are hereby incorporated by reference. The totalamount of water that may be fed to the vaporizer is at least 0.01 wt. %,e.g., at least 0.1 wt. % or at least 1 wt. %. In terms of ranges, thetotal amount of water that may be fed to the vaporizer is from 0.01 wt.% to 20 wt. %, e.g., from 0.1 wt. % to 15 wt. % or from 1 wt. % to 15wt. %. In some embodiments, more water is fed to the vaporizer thanethanol, on a molar basis.

In some embodiments, acetic acid stream and/or the liquid recycle streammay comprise water. Thus, a separate water stream may not be needed.

When the liquid recycle stream, acetic acid stream and water stream arefed to the vaporizer to yield a feed stream, the total amount of waterfed to the vaporizer is at least 0.01 wt. %. The feed stream from thevaporizer is then fed to the reactor. Due to the presence of both ethylacetate and acetic acid in the feed stream, the catalyst in the reactorpreferably converts both ethyl acetate and acetic acid. For purposes ofthe present invention, the catalyst is at least a bifunctional catalyst.Generally, the conversion of acetic acid is relatively larger than theconversion of ethyl acetate. To maintain sufficient conversion of ethylacetate, the present invention feeds water to the vaporizer to promoteconversion of ethyl acetate. Although feeding water to the vaporizerincreases ethyl acetate conversion, feeding additional water does notsignificantly impact the acetic acid conversion.

It has surprisingly and unexpectedly been found that by feeding at least0.01 wt. % water to the vaporizer when ethyl acetate conversion isnegative, ethyl acetate conversion is increased to above 0%, e.g., is atleast 1%, at least 3% or at least 15%. One theory for this is that thewater helps to promote the deactivated catalyst in the reactor.

In some embodiments, a monitoring device may be used to determine whenethyl acetate conversion is negative, e.g., when there is a net increasein ethyl acetate from the feed stream going into the reactor compared tothe crude ethanol product exiting the reactor. When ethyl acetateconversion is negative, water may be fed to the vaporizer to increaseethyl acetate conversion to above 0%, e.g., to above 1%, to above 5% orto above 15%.

In one embodiment, the volumetric ratio of acetic acid stream to liquidrecycle stream may be at least 1.5:1, e.g., at least 2:1 or at least5:1. In terms of ranges, the volumetric ratio of acetic acid stream toliquid recycle stream is from 1.5:1 to 20:1, e.g., from 1.5:1 to 5:1.Generally, the molar ratio of acetic acid to ethyl acetate in thevaporizer is greater than 1:1, e.g., greater than 1.5:1 or greater than2:1. The vaporizer may be operate at a temperature from 20° C. to 300°C. and may operate at a pressure from 10 kPa to 3000 kPa. In someembodiments, under the conditions in the vaporizer, a non-catalyzedreaction may occur to drive the formation of additional ethyl acetateand reduce the amount of fresh acetic acid. Without being bound bytheory the presence of water in the feed water may also suppress theformation of ethyl acetate. In addition, because the vapor feed streammay be further heated prior to the reactor, additional undesiredesterification of the fresh acetic acid in the feed stream may occur.Generally, the vapor feed stream exits the vaporizer at a temperature ofabout 120° C. and is further heated to a temperature of about 275° C.before entering the reactor. Typically, lowering the temperature of thevapor stream feed would reduce the formation of additional ethylacetate. However, because of the pre-heating step required in thepresent processes, the formation of ethyl acetate cannot be controlledby cooling the vapor stream feed and thus more ethyl acetate is fed tothe reactor.

In recovering ethanol, the processes of the present invention may usetwo or more distillation columns. In one embodiment, a firstdistillation column is used to separate the feed stream into a residuestream comprising acetic acid. Depending on where the ethanol isconcentration, either in the distillate or residue, the streamcontaining the ethanol from the first distillation column may besubsequently separated to obtain ethanol. The remaining streams may bereturned to the vaporizer as the liquid recycle streams. There may be atleast one liquid recycle stream that comprises ethyl acetate from thisseparation.

In another embodiment, a first distillation column is used to separatethe feed stream into a residue stream comprising water and acetic acidfrom the crude ethanol product and a distillate stream comprisingethanol, acetaldehyde and ethyl acetate. The residue may comprise asubstantial portion of the water. In one embodiment, 30 to 90% of thewater in the crude ethanol product is removed in the residue, e.g., from40 to 88% of the water or from 50 to 84% of the water. Water may also beremoved from the distillate to form an ethanol mixture stream,preferably comprising less than 10 wt. % water, less than 6 wt. % wateror less than 4 wt. % water. In terms of ranges the ethanol mixturestream comprises from 0.001 to 10 wt. % water, e.g., from 0.01 to 6 wt.% water or from 0.1 to 4 wt. % water. Water may be removed, for example,using an adsorption unit, membrane, molecular sieves, extractive columndistillation, or a combination thereof. Suitable adsorption unitsinclude pressure swing adsorption (PSA) units and thermal swingadsorption (TSA) units. The adsorption units may comprise molecularsieves, such as aluminosilicate compounds. Product ethanol is thenrecovered from the ethanol mixture stream. There may be at least oneliquid recycle stream that comprises ethyl acetate that is alsorecovered from the ethanol mixture stream.

In another embodiment, a first distillation column is used to separatethe feed stream into a residue stream comprising ethanol, ethyl acetate,water and acetic acid from the crude ethanol product and a distillatestream comprising acetaldehyde and ethyl acetate. The distillate may beat least one liquid recycle stream. The residue stream, for example, maycomprise at least 50% of the ethanol from the crude ethanol product, andmore preferably at least 70%. In terms of ranges, the residue stream maycomprise from 50% to 99.9% of the ethanol from the crude ethanolproduct, and more preferably from 70% to 99%. The amount of ethanol fromthe crude ethanol recovered in the residue may be greater than 97.5%,e.g. greater than 99%. The residue may also comprise a substantialportion of the water and acetic acid from the crude ethanol product. Theresidue stream comprising ethanol, ethyl acetate, water, and acetic acidmay be further separated to recover ethanol. Because these compounds maynot be in equilibrium, additional ethyl acetate may be produced throughesterification of ethanol and acetic acid. In one preferred embodiment,the water and acetic acid may be removed as another residue stream in aseparate distillation column. In addition, the water carried over in theseparate distillation column may be removed with a water separator thatis selected from the group consisting of an adsorption unit, membrane,extractive column distillation, molecular sieves, and combinationsthereof.

Although ethyl acetate is partially withdrawn into the first distillate,a higher ethyl acetate concentration in the first residue leads toincreased ethanol concentration in the first residue and decreasedethanol concentrations in the first distillate. Thus, overall ethanolrecovery may be increased. Depending on the ethyl acetate concentrationin the residue and whether there is in situ esterification in theresidue or an esterification reactor, it may be necessary to furtherseparate the ethyl acetate and ethanol in a separate column. Preferably,this separate column is located after the water has been removed using adistillation column and/or water separator. Generally, a separate columnmay be necessary when the residue comprises at least 50 wppm ethylacetate or there is in situ esterification. When the ethyl acetate isless than 50 wppm, it may not be necessary to use separate column toseparate ethyl acetate and ethanol.

Ethyl acetate may be separated from ethanol in a separate column nearthe end of the purification process. In removing ethyl acetate,additional light organics may also be removed, thus improving thequality of the ethanol product by decreasing impurities. Preferably,water and/or acetic acid may be removed prior to the ethylacetate/ethanol separation. In one embodiment, after the ethyl acetateis separated from ethanol, the ethyl acetate is returned to the initialcolumn and fed near the top of that column. This allows for any ethanolremoved with the ethyl acetate to be recovered and further reduces theamount of ethanol being recycled to the reactor. In some embodiments, itis preferably to recycle ethanol within the separation zone but todecrease the amount of ethanol recycled to the reactor. Decreasing theamount of ethanol recycled to the reactor may reduce reactor capital andimprove efficiency in recovering ethanol. Preferably, the ethyl acetateis removed in the distillate of the first column and returned to thereactor with the acetaldehyde.

In preferred embodiments, the residue stream of the first columncomprises a substantial portion of the water and the acetic acid fromthe crude ethanol stream. The residue stream may comprise at least 80%of the water from the crude ethanol stream, and more preferably at least90%. In terms of ranges, the residue stream preferably comprises from80% to 100% of the water from the crude ethanol stream, and morepreferably from 90% to 99.4%. The residue stream may comprise at least85% of the acetic acid from the crude ethanol stream, e.g., at least 90%and more preferably about 100%. In terms of ranges, the residue streampreferably comprises from 85% to 100% of the acetic acid from the crudeethanol stream, and more preferably from 90% to 100%. In one embodiment,substantially all of the acetic acid is recovered in the residue stream.

In one embodiment, each of the columns is sized to be capital andeconomically feasible for the rate of ethanol production. The totaldiameter for the columns used to separate the crude ethanol stream maybe from 5 to 40 meters, e.g., from 10 to 30 meters or from 12 to 20meters. Each column may have a varying size. In one embodiment, theratio of column diameter in meters for all the distillation columns totons of ethanol produced per hour is from 1:2 to 1:30, e.g., from 1:3 to1:20 or from 1:4 to 1:10. This would allow the process to achieveproduction rates of 25 to 250 tons of ethanol per hour.

The distillate from the initial column comprises light organics, such asacetaldehyde, diethyl acetal, acetone and ethyl acetate. In addition,minor amounts of ethanol and water may be present in the distillate.Removing these light organic components from the crude ethanol stream inthe initial column provides an efficient means for removing acetaldehydeand ethyl acetate. In addition, acetaldehyde, diethyl acetal and acetoneare not carried over with the ethanol when multiple columns are used,thus reducing the formation of byproducts from acetaldehyde, diethylacetal, and acetone. In particular, acetaldehyde and/or ethyl acetatemay be returned to the reactor, and converted to additional ethanol. Inanother embodiment, a purge may remove these light organics from thesystem.

The residue from the initial column comprises ethyl acetate. Althoughethyl acetate is also partially withdrawn into the first distillate, ahigher ethyl acetate concentration in the first residue leads toincreased ethanol concentration in the first residue and decreaseethanol concentrations in the first distillate. Thus overall ethanolrecovery may be increased. Ethyl acetate may be separated from ethanolin a separate column near the end of the purification process. Inremoving ethyl acetate, additional light organics may also be removedand thus improve the quality of the ethanol product by decreasingimpurities. Preferably, water and/or acetic acid may be removed prior tothe ethyl acetate/ethanol separation.

In one embodiment, after the ethyl acetate is separated from ethanol,the ethyl acetate is returned to the initial column and fed near the topof that column. This allows for any ethanol removed with the ethylacetate to be recovered and further reduces the amount of ethanol beingrecycled to the reactor. Decreasing the amount of ethanol recycled tothe reactor may reduce reactor capital and improve efficiency inrecovering ethanol. Preferably, the ethyl acetate is removed in thedistillate of the first column and returned to the reactor with theacetaldehyde.

In another embodiment, the present invention is directed to a processfor producing ethanol, comprising hydrogenating a feed stream in areactor in the presence of a catalyst to form a crude ethanol product.At least a portion of the crude ethanol product may then be separated intwo or more columns to produce ethanol and a liquid recycle streamcomprising ethyl acetate, wherein the feed stream is produced bycombining an acetic acid stream and a liquid recycle stream. The processfurther comprises maintaining a water concentration in the feed streamand maintaining a constant ethyl acetate concentration in the reactor.During the process, when the ethyl acetate conversion is less than 0%,e.g., more ethyl acetate is present in the crude product stream than inthe feed stream, the process further comprises adding excess water tothe feed stream to maintain the constant ethyl acetate concentration.

Hydrogenation of Acetic Acid

The process of the present invention may be used with any hydrogenationprocess for producing ethanol. The materials, catalysts, reactionconditions, and separation processes that may be used in thehydrogenation of acetic acid are described further below.

The raw materials, acetic acid and hydrogen, fed to the reactor used inconnection with the process of this invention may be derived from anysuitable source including natural gas, petroleum, coal, biomass, and soforth. As examples, acetic acid may be produced via methanolcarbonylation, acetaldehyde oxidation, ethane oxidation, oxidativefermentation, and anaerobic fermentation. Methanol carbonylationprocesses suitable for production of acetic acid are described in U.S.Pat. Nos. 7,208,624; 7,115,772; 7,005,541; 6,657,078; 6,627,770;6,143,930; 5,599,976; 5,144,068; 5,026,908; 5,001,259; and 4,994,608,the entire disclosures of which are incorporated herein by reference.Optionally, the production of ethanol may be integrated with suchmethanol carbonylation processes.

As petroleum and natural gas prices fluctuate becoming either more orless expensive, methods for producing acetic acid and intermediates suchas methanol and carbon monoxide from alternate carbon sources have drawnincreasing interest. In particular, when petroleum is relativelyexpensive, it may become advantageous to produce acetic acid fromsynthesis gas (“syngas”) that is derived from more available carbonsources. U.S. Pat. No. 6,232,352, the entirety of which is incorporatedherein by reference, for example, teaches a method of retrofitting amethanol plant for the manufacture of acetic acid. By retrofitting amethanol plant, the large capital costs associated with CO generationfor a new acetic acid plant are significantly reduced or largelyeliminated. All or part of the syngas is diverted from the methanolsynthesis loop and supplied to a separator unit to recover CO, which isthen used to produce acetic acid. In a similar manner, hydrogen for thehydrogenation step may be supplied from syngas.

In some embodiments, some or all of the raw materials for theabove-described acetic acid hydrogenation process may be derivedpartially or entirely from syngas. For example, the acetic acid may beformed from methanol and carbon monoxide, both of which may be derivedfrom syngas. The syngas may be formed by partial oxidation reforming orsteam reforming, and the carbon monoxide may be separated from syngas.Similarly, hydrogen that is used in the step of hydrogenating the aceticacid to form the crude ethanol product may be separated from syngas. Thesyngas, in turn, may be derived from variety of carbon sources. Thecarbon source, for example, may be selected from the group consisting ofnatural gas, oil, petroleum, coal, biomass, and combinations thereof.Syngas or hydrogen may also be obtained from bio-derived methane gas,such as bio-derived methane gas produced by landfills or agriculturalwaste.

Biomass-derived syngas has a detectable ¹⁴C isotope content as comparedto fossil fuels such as coal or natural gas. An equilibrium forms in theEarth's atmosphere between constant new formation and constantdegradation, and so the proportion of the ¹⁴C nuclei in the carbon inthe atmosphere on Earth is constant over long periods. The samedistribution ratio n¹⁴C:n¹²C ratio is established in living organisms asis present in the surrounding atmosphere, which stops at death and ¹⁴Cdecomposes at a half life of about 6000 years. Methanol, acetic acidand/or ethanol formed from biomass-derived syngas would be expected tohave a ¹⁴C content that is substantially similar to living organisms.For example, the ¹⁴C:¹²C ratio of the methanol, acetic acid and/orethanol may be from one half to about 1 of the ¹⁴C:¹²C ratio for livingorganisms. In other embodiments, the syngas, methanol, acetic acidand/or ethanol described herein are derived wholly from fossil fuels,i.e. carbon sources produced over 60,000 years ago, may have nodetectable ¹⁴C content.

In another embodiment, the acetic acid used in the hydrogenation stepmay be formed from the fermentation of biomass. The fermentation processpreferably utilizes an acetogenic process or a homoacetogenicmicroorganism to ferment sugars to acetic acid producing little, if any,carbon dioxide as a by-product. The carbon efficiency for thefermentation process preferably is greater than 70%, greater than 80% orgreater than 90% as compared to conventional yeast processing, whichtypically has a carbon efficiency of about 67%. Optionally, themicroorganism employed in the fermentation process is of a genusselected from the group consisting of Clostridium, Lactobacillus,Moorella, Thermoanaerobacter, Propionibacterium, Propionispera,Anaerobiospirillum, and Bacteriodes, and in particular, species selectedfrom the group consisting of Clostridium formicoaceticum, Clostridiumbutyricum, Moorella thermoacetica, Thermoanaerobacter kivui,Lactobacillus delbrukii, Propionibacterium acidipropionici,Propionispera arboris, Anaerobiospirillum succinicproducens, Bacteriodesamylophilus and Bacteriodes ruminicola. Optionally in this process, allor a portion of the unfermented residue from the biomass, e.g., lignans,may be gasified to form hydrogen that may be used in the hydrogenationstep of the present invention. Exemplary fermentation processes forforming acetic acid are disclosed in U.S. Pat. Nos. 6,509,180;6,927,048; 7,074,603; 7,507,562; 7,351,559; 7,601,865; 7,682,812; and7,888,082, the entireties of which are incorporated herein by reference.See also U.S. Pub. Nos. 2008/0193989 and 2009/0281354, the entireties ofwhich are incorporated herein by reference.

Examples of biomass include, but are not limited to, agriculturalwastes, forest products, grasses, and other cellulosic material, timberharvesting residues, softwood chips, hardwood chips, tree branches, treestumps, leaves, bark, sawdust, off-spec paper pulp, corn, corn stover,wheat straw, rice straw, sugarcane bagasse, switchgrass, miscanthus,animal manure, municipal garbage, municipal sewage, commercial waste,grape pumice, almond shells, pecan shells, coconut shells, coffeegrounds, grass pellets, hay pellets, wood pellets, cardboard, paper,plastic, and cloth. See, e.g., U.S. Pat. No. 7,884,253, the entirety ofwhich is incorporated herein by reference. Another biomass source isblack liquor, a thick, dark liquid that is a byproduct of the Kraftprocess for transforming wood into pulp, which is then dried to makepaper. Black liquor is an aqueous solution of lignin residues,hemicellulose, and inorganic chemicals.

U.S. Pat. No. RE 35,377, also incorporated herein by reference, providesa method for the production of methanol by conversion of carbonaceousmaterials such as oil, coal, natural gas and biomass materials. Theprocess includes hydrogasification of solid and/or liquid carbonaceousmaterials to obtain a process gas which is steam pyrolized withadditional natural gas to form synthesis gas. The syngas is converted tomethanol which may be carbonylated to acetic acid. The method likewiseproduces hydrogen which may be used in connection with this invention asnoted above. U.S. Pat. No. 5,821,111, which discloses a process forconverting waste biomass through gasification into synthesis gas, andU.S. Pat. No. 6,685,754, which discloses a method for the production ofa hydrogen-containing gas composition, such as a synthesis gas includinghydrogen and carbon monoxide, are incorporated herein by reference intheir entireties.

The acetic acid feed to the hydrogenation reactor may also compriseother carboxylic acids and anhydrides, as well as aldehyde and/orketones, such as acetaldehyde and acetone. Preferably, a suitable aceticacid feed stream comprises one or more of the compounds selected fromthe group consisting of acetic acid, acetic anhydride, acetaldehyde,ethyl acetate, and mixtures thereof. These other compounds may also behydrogenated in the processes of the present invention. In someembodiments, the presence of carboxylic acids, such as propanoic acid orits anhydride, may be beneficial in producing propanol. In accordancewith embodiments of the present invention, water may also be present inthe acetic acid feed. Preferably, the feed to the hydrogenation reactordoes not comprise syngas or a mixture of hydrogen, carbon monoxide,and/or carbon dioxide that would be similar to syngas. In otherembodiments, the feed to the hydrogenation reactor does not containalkanes including linear or cyclic alkane, such as ethane and/orcyclohexane.

Alternatively, acetic acid in vapor form may be taken directly as crudeproduct from the flash vessel of a methanol carbonylation unit of theclass described in U.S. Pat. No. 6,657,078, the entirety of which isincorporated herein by reference. The crude vapor product, for example,may be fed directly to the hydrogenation reactor without the need forcondensing the acetic acid and light ends or removing water, savingoverall processing costs.

The acetic acid may be vaporized at the reaction temperature, followingwhich the vaporized acetic acid may be fed along with hydrogen in anundiluted state or diluted with a relatively inert carrier gas, such asnitrogen, argon, helium, carbon dioxide and the like. For reactions runin the vapor phase, the temperature should be controlled in the systemsuch that it does not fall below the dew point of acetic acid. In oneembodiment, the acetic acid may be vaporized at the boiling point ofacetic acid at the particular pressure, and then the vaporized aceticacid may be further heated to the reactor inlet temperature. In anotherembodiment, the acetic acid is mixed with other gases before vaporizing,followed by heating the mixed vapors up to the reactor inlettemperature. Preferably, the acetic acid is transferred to the vaporstate by passing hydrogen and/or recycle gas through the acetic acid ata temperature at or below 125° C., followed by heating of the combinedgaseous stream to the reactor inlet temperature.

Some embodiments of the process of hydrogenating acetic acid to formethanol may include a variety of configurations using a fixed bedreactor or a fluidized bed reactor. In many embodiments of the presentinvention, an “adiabatic” reactor can be used; that is, there is littleor no need for internal plumbing through the reaction zone to add orremove heat. In other embodiments, a radial flow reactor or reactors maybe employed as the reactor, or a series of reactors may be employed withor without heat exchange, quenching, or introduction of additional feedmaterial. Alternatively, a shell and tube reactor provided with a heattransfer medium may be used. In many cases, the reaction zone may behoused in a single vessel or in a series of vessels with heat exchangerstherebetween.

In preferred embodiments, the catalyst is employed in a fixed bedreactor, e.g., in the shape of a pipe or tube, where the reactants,typically in the vapor form, are passed over or through the catalyst.Other reactors, such as fluid or ebullient bed reactors, can beemployed. In some instances, the hydrogenation catalysts may be used inconjunction with an inert material to regulate the pressure drop of thereactant stream through the catalyst bed and the contact time of thereactant compounds with the catalyst particles.

The hydrogenation in the reactor may be carried out in either the liquidphase or vapor phase. Preferably, the reaction is carried out in thevapor phase under the following conditions. The reaction temperature mayrange from 125° C. to 350° C., e.g., from 200° C. to 325° C., from 225°C. to 300° C., or from 250° C. to 300° C. The reactor pressure may rangefrom 10 kPa to 3000 kPa, e.g., from 50 kPa to 2300 kPa, or from 100 kPato 1500 kPa. The reactants may be fed to the reactor at a gas hourlyspace velocity (GHSV) of greater than 500 hr⁻¹, e.g., greater than 1000hr⁻¹, greater than 2500 hr⁻¹ or even greater than 5000 hr⁻¹. In terms ofranges the GHSV may range from 50 hr⁻¹ to 50,000 hr⁻¹, e.g., from 500hr⁻¹ to 30,000 hr⁻¹, from 1000 hr⁻¹ to 10,000 hr⁻¹, or from 1000 hr⁻¹ to6500 hr⁻¹.

The hydrogenation optionally is carried out at a pressure justsufficient to overcome the pressure drop across the catalytic bed at theGHSV selected, although there is no bar to the use of higher pressures,it being understood that considerable pressure drop through the reactorbed may be experienced at high space velocities, e.g., 5000 hr⁻¹ or6,500 hr⁻¹.

Although the reaction consumes two moles of hydrogen per mole of aceticacid to produce one mole of ethanol, the actual molar ratio of hydrogento acetic acid in the feed stream may vary from about 100:1 to 1:100,e.g., from 50:1 to 1:50, from 20:1 to 1:2, or from 18:1 to 2:1. Mostpreferably, the molar ratio of hydrogen to acetic acid is greater than2:1, e.g., greater than 4:1 or greater than 8:1.

Contact or residence time can also vary widely, depending upon suchvariables as amount of acetic acid, catalyst, reactor, temperature, andpressure. Typical contact times range from a fraction of a second tomore than several hours when a catalyst system other than a fixed bed isused, with preferred contact times, at least for vapor phase reactions,from 0.1 to 100 seconds, e.g., from 0.3 to 80 seconds or from 0.4 to 30seconds.

The hydrogenation of acetic acid to form ethanol is preferably conductedin the presence of a hydrogenation catalyst in the reactor. Thehydrogenation catalyst is preferably a bifunctional catalyst and mayconvert acetic acid and ethyl acetate. The catalysts preferably are notmethanol synthesis catalysts and are substantially free of copper and/orzinc, including oxides thereof. Suitable hydrogenation catalysts includecatalysts comprising a first metal and optionally one or more of asecond metal, a third metal or any number of additional metals,optionally on a catalyst support. Preferred bimetallic combinations forsome exemplary catalyst compositions include platinum/tin,platinum/ruthenium, platinum/rhenium, palladium/ruthenium,palladium/rhenium, cobalt/palladium, cobalt/platinum, cobalt/chromium,cobalt/ruthenium, cobalt/tin, silver/palladium, nickel/palladium,gold/palladium, ruthenium/rhenium, and ruthenium/iron. Additional metalcombinations may include palladium/rhenium/tin,palladium/rhenium/cobalt, palladium/rhenium/nickel,platinum/tin/palladium, platinum/tin/cobalt, platinum/tin/chromium, andplatinum/tin/nickel.

The hydrogenation of acetic acid to form ethanol is preferably conductedin the presence of a hydrogenation catalyst. Exemplary catalysts arefurther described in U.S. Pat. Nos. 7,608,744 and 7,863,489, and U.S.Pub. Nos. 2010/0121114 and 2010/0197985, the entireties of which areincorporated herein by reference. In another embodiment, the catalystcomprises a Co/Mo/S catalyst of the type described in U.S. Pub. No.2009/0069609, the entirety of which is incorporated herein by reference.In some embodiments the catalyst may be a bulk catalyst.

In one embodiment, the catalyst comprises a first metal selected fromthe group consisting of iron, cobalt, nickel, ruthenium, rhodium,palladium, osmium, iridium, platinum, titanium, chromium, rhenium,molybdenum, and tungsten. Preferably, the first metal is selected fromthe group consisting of platinum, palladium, cobalt, nickel, andruthenium. More preferably, the first metal is selected from platinumand palladium. In embodiments of the invention where the first metalcomprises platinum, it is preferred that the catalyst comprises platinumin an amount less than 5 wt. %, e.g., less than 3 wt. % or less than 1wt. %, due to the high commercial demand for platinum.

As indicated above, in some embodiments, the catalyst further comprisesa second metal, which typically would function as a promoter. Ifpresent, the second metal preferably is selected from the groupconsisting of molybdenum, tin, chromium, iron, cobalt, vanadium,tungsten, palladium, platinum, lanthanum, cerium, manganese, ruthenium,rhenium, gold, and nickel. More preferably, the second metal is selectedfrom the group consisting of copper, tin, cobalt, rhenium, and nickel.More preferably, the second metal is selected from tin and rhenium.

In certain embodiments where the catalyst includes two or more metals,e.g., a first metal and a second metal, the first metal is present inthe catalyst in an amount from 0.1 to 10 wt. %, e.g., from 0.1 to 5 wt.%, or from 0.1 to 3 wt. %. The second metal preferably is present in anamount from 0.1 to 20 wt. %, e.g., from 0.1 to 10 wt. %, or from 0.1 to7.5 wt. %. For catalysts comprising two or more metals, the two or moremetals may be alloyed with one another or may comprise a non-alloyedmetal solution or mixture.

The catalyst may also comprise a third metal selected from any of themetals listed above in connection with the first or second metal, solong as the third metal is different from the first and second metals.In preferred aspects, the third metal is selected from the groupconsisting of cobalt, palladium, ruthenium, platinum, tin, and rhenium.More preferably, the third metal is selected from cobalt, palladium, andruthenium. When present, the total weight of the third metal preferablyis from 0.1 to 20 wt. %, e.g., from 0.1 to 10 wt. %, or from 0.1 to 7.5wt. %. In one embodiment, the catalyst may comprise platinum, tin andcobalt.

In addition to one or more metals, in some embodiments of the presentinvention the catalysts further comprise a support or a modifiedsupport. As used herein, the term “modified support” refers to a supportthat includes a support material and a support modifier, which adjuststhe acidity of the support material.

The total weight of the support or modified support, based on the totalweight of the catalyst, preferably is from 75 to 99.9 wt. %, e.g., from78 to 99 wt. %, or from 80 to 97.5 wt. %. In preferred embodiments thatutilize a modified support, the support modifier is present in an amountfrom 0.1 to 50 wt. %, e.g., from 0.2 to 25 wt. %, from 1 to 20 wt. %, orfrom 3 to 15 wt. %, based on the total weight of the catalyst. Themetals of the catalysts may be dispersed throughout the support, layeredthroughout the support, coated on the outer surface of the support(i.e., egg shell), or decorated on the surface of the support.

As will be appreciated by those of ordinary skill in the art, supportmaterials are selected such that the catalyst system is suitably active,selective and robust under the process conditions employed for theformation of ethanol.

Suitable support materials may include, for example, stable metaloxide-based supports or ceramic-based supports. Preferred supportsinclude silicaceous supports, such as silica, silica gel,silica/alumina, a Group IIA silicate such as calcium metasilicate,pyrogenic silica, high purity silica, and mixtures thereof. Othersupports may include, but are not limited to, iron oxide, alumina,titania, zirconia, magnesium oxide, carbon, graphite, high surface areagraphitized carbon, activated carbons, and mixtures thereof.

As indicated, the catalyst support may be modified with a supportmodifier. In some embodiments, the support modifier may be an acidicmodifier that increases the acidity of the catalyst. Suitable acidicsupport modifiers may be selected from the group consisting of: oxidesof Group IVB metals, oxides of Group VB metals, oxides of Group VIBmetals, oxides of Group VIIB metals, oxides of Group VIIIB metals,aluminum oxides, and mixtures thereof. Acidic support modifiers includethose selected from the group consisting of TiO₂, ZrO₂, Nb₂O₅, Ta₂O₅,Al₂O₃, B₂O₃, P₂O₅, and Sb₂O₃. Preferred acidic support modifiers includethose selected from the group consisting of TiO₂, ZrO₂, Nb₂O₅, Ta₂O₅,and Al₂O₃. The acidic modifier may also include WO₃, MoO₃, Fe₂O₃, Cr₂O₃,V₂O₅, MnO₂, CuO, Co₂O₃, and Bi₂O₃.

In another embodiment, the support modifier may be a basic modifier thathas a low volatility or no volatility. Such basic modifiers, forexample, may be selected from the group consisting of: (i) alkalineearth metal oxides, (ii) alkali metal oxides, (iii) alkaline earth metalmetasilicates, (iv) alkali metal metasilicates, (v) Group IIIB metaloxides, (vi) Group IIIB metal metasilicates, and mixtures thereof. Inaddition to oxides and metasilicates, other types of modifiers includingnitrates, nitrites, acetates, and lactates may be used. Preferably, thesupport modifier is selected from the group consisting of oxides andmetasilicates of any of sodium, potassium, magnesium, calcium, scandiumand yttrium, as well as mixtures of any of the foregoing. Morepreferably, the basic support modifier is a calcium silicate, and evenmore preferably calcium metasilicate (CaSiO₃). The calcium metasilicatemay be crystalline or amorphous.

The catalyst compositions suitable for use with the present inventionpreferably are formed through metal impregnation of the modifiedsupport, although other processes such as chemical vapor deposition mayalso be employed. Such impregnation techniques are described in U.S.Pat. Nos. 7,608,744 and 7,863,489 and U.S. Pub. No. 2010/0197985referred to above, the entireties of which are incorporated herein byreference.

After the washing, drying and calcining of the catalyst is completed,the catalyst may be reduced in order to activate the catalyst. Reductionis carried out in the presence of a reducing gas, preferably hydrogen.The reducing gas is continuously passed over the catalyst at an initialambient temperature that is increased up to 400° C. In one embodiment,the reduction is preferably carried out after the catalyst has beenloaded into the reaction vessel where the hydrogenation will be carriedout.

In particular, the hydrogenation of acetic acid may achieve favorableconversion of acetic acid and ethyl acetate, and favorable selectivityand productivity to ethanol. For purposes of the present invention, theterm “conversion” refers to the amount of acetic acid or ethyl acetatein the feed that is converted to a compound other than acetic acid orethyl acetate, respectively. Conversion is expressed as a percentagebased on acetic acid or ethyl acetate in the feed. The conversion ofacetic acid may be at least 40%, e.g., at least 50%, at least 60%, atleast 70% or at least 80%. The conversion of ethyl acetate acidpreferably is greater than 0%, meaning that more ethyl acetate isconsumed than produced. During the hydrogenation of acetic acid, ethylacetate may be produced. If the ethyl acetate produced is greater thanthe ethyl acetate consumed, the conversion of ethyl acetate would benegative. However, for purposes of the present invention, enough of theethyl acetate is consumed to at least offset the produced ethyl acetate.Thus, preferably conversion of ethyl acetate may be at least 0%, e.g.,at least 5%, at least 10%, at least 20%, or at least 35%. Althoughcatalysts that have high conversions are desirable, especially aceticacid conversions that are at least 80% or at least 90%, in someembodiments a low acetic acid conversion may be acceptable at highselectivity for ethanol.

As indicated above, the present invention may determine when the ethylacetate conversion is low or negative which indicates a decrease incatalyst activity. To maintain catalyst activity, water may be fed tothe hydrogenation reactor. This advantageously promotes ethyl acetateconversion without impairing acetic acid conversion.

Selectivity is expressed as a mole percent based on converted aceticacid and/or ethyl acetate. It should be understood that each compoundconverted from acetic acid and/or ethyl acetate has an independentselectivity and that selectivity is independent from conversion. Forexample, if 60 mole % of the converted acetic acid is converted toethanol, we refer to the ethanol selectivity as 60%. The totalselectivity is based on the combined converted acetic acid and ethylacetate. Preferably, the catalyst total selectivity to ethanol is atleast 60%, e.g., at least 70%, or at least 80%. Preferably, the totalselectivity to ethanol is at least 80%, e.g., at least 85% or at least88%. Preferred embodiments of the hydrogenation process also have lowselectivity to undesirable products, such as methane, ethane, and carbondioxide. The selectivity to these undesirable products preferably isless than 4%, e.g., less than 2% or less than 1%. More preferably, theseundesirable products are present in undetectable amounts. Formation ofalkanes may be low, and ideally less than 2%, less than 1%, or less than0.5% of the acetic acid passed over the catalyst is converted toalkanes, which have little value other than as fuel.

The term “productivity,” as used herein, refers to the grams of aspecified product, e.g., ethanol, formed during the hydrogenation basedon the kilograms of catalyst used per hour. The productivity preferablymay range from 100 to 3,000 grams of ethanol per kilogram of catalystper hour.

In various embodiments of the present invention, the crude ethanolproduct produced by the reactor, before any subsequent processing, suchas purification and separation, will typically comprise unreacted aceticacid, ethanol and water. Exemplary compositional ranges for the crudeethanol product are provided in Table 1. The “others” identified inTable 1 may include, for example, esters, ethers, aldehydes, ketones,alkanes, and carbon dioxide.

TABLE 1 CRUDE ETHANOL PRODUCT COMPOSITIONS Conc. Conc. Conc. Conc.Component (wt. %) (wt. %) (wt. %) (wt. %) Ethanol 5 to 72 15 to 72  15to 70 25 to 65 Acetic Acid 0 to 90 0 to 50  0 to 35  0 to 15 Water 5 to50 5 to 45 10 to 40 10 to 35 Ethyl Acetate 0 to 30 1 to 25  3 to 20  5to 18 Acetaldehyde 0 to 10 0 to 3  0.1 to 3   0.2 to 2   Others 0.1 to10   0.1 to 6   0.1 to 4   —

In one embodiment, the crude ethanol product may comprise acetic acid inan amount less than 20 wt. %, e.g., less than 15 wt. %, less than 10 wt.% or less than 5 wt. %. In terms of ranges, the acetic acidconcentration of Table 1 may range from 0.1 wt. % to 20 wt. %, e.g., 0.2wt. % to 15 wt. %, from 0.5 wt. % to 10 wt. % or from 1 wt. % to 5 wt.%. In embodiments having lower amounts of acetic acid, the conversion ofacetic acid is preferably greater than 75%, e.g., greater than 85% orgreater than 90%. In addition, the selectivity to ethanol may also bepreferably high, and is greater than 75%, e.g., greater than 85% orgreater than 90%.

Ethanol Separation

Ethanol produced by the reactor may be recovered using several differenttechniques. In FIG. 1, the separation of the crude ethanol product usesfour columns. In FIG. 2, the crude ethanol product is separated in twocolumns with an intervening water separation. In FIG. 3, the separationof the crude ethanol product uses two columns. Other separation systemsmay also be used with embodiments of the present invention.

Hydrogenation system 100 includes a reaction zone 101 and separationzone 102. Fresh acetic acid in line 105 and a liquid recycle stream fromseparation zone 102, shown by line 113 in FIG. 1 are mixed prior tovaporizer 106 to form a mixed feed in line 117. As stated herein, liquidrecycle stream in line 113 comprises ethyl acetate. Preferably, theliquid recycle stream is a distillate stream from separation zone 102.Depending on the water concentration of fresh acetic acid in line 105and liquid recycle stream, an optional water stream in line 116 may befed directly to vaporizer 106 or may be combined with mixed feed in line117. As indicated above, the total water concentration fed to vaporizer106 from lines 105, 117, or optional line 116 is greater than 0.01 wt.%, preferably from 0.01 to 20 wt. %. Hydrogen in line 104 and mixed feedin line 117 are fed to vaporizer 106 to create a vapor feed stream inline 107 that is directed to reactor 108. Hydrogen feed line 104 may bepreheated to a temperature from 30° C. to 150° C., e.g., from 50° C. to125° C. or from 60° C. to 115° C. Hydrogen feed line 104 may be fed at apressure similar to the reactor pressure, such as from 10 kPa to 3000kPa, e.g., from 50 kPa to 2300 kPa, or from 100 kPa to 2100 kPa. In oneembodiment, lines 104 and 114 may be combined and jointly fed to thevaporizer 106.

Vaporizer 106 may operate at a temperature from 20° C. to 300° C. and ata pressure from 10 kPa to 3000 kPa. Vaporizer 106 produces vapor feedstream in line 107 by transferring the acetic acid, ethyl acetate, andwater from the liquid to gas phase below the boiling point of aceticacid in reactor 108 at the operating pressure of the reactor. In oneembodiment, the acetic acid in the liquid state is maintained at atemperature below 160° C., e.g., below 150° C. or below 130° C.Vaporizer 106 may be operated at a temperature of at least 118° C.

The temperature of feed stream in line 107 is preferably from 100° C. to350° C., e.g., from 120° C. to 310° C. or from 150° C. to 300° C. Apreheater 115 may be used to further heat the feed stream in line 107 tothe reactor temperature.

Any feed that is not vaporized is removed from vaporizer 106 in ablowdown stream and may be recycled or discarded thereto. The mass ratioof feed stream in line 107 to blowdown stream may be from 6:1 to 500:1,e.g., from 10:1 to 500:1, from 20:1 to 500:1 or from 50:1 to 500:1.

Although line 107 is shown as being directed to the top of reactor 108,line 107 may be directed to the side, upper portion, or bottom ofreactor 108. Reactor 108 contains the catalyst that is used in thehydrogenation of the carboxylic acid, preferably acetic acid. In oneembodiment, one or more guard beds (not shown) may be used upstream ofthe reactor, optionally upstream of the vaporizer 106, to protect thecatalyst from poisons or undesirable impurities contained in the feed orreturn/recycle streams. Such guard beds may be employed in the vapor orliquid streams. Suitable guard bed materials may include, for example,carbon, silica, alumina, ceramic, or resins. In one aspect, the guardbed media is functionalized, e.g., silver functionalized, to trapparticular species such as sulfur or halogens. During the hydrogenationprocess, a crude ethanol product is withdrawn, preferably continuously,from reactor 108 via line 109.

The crude ethanol product in line 109 may be condensed and fed to aseparator 110, which, in turn, provides a vapor stream 111 and a liquidstream 112. In some embodiments, separator 110 may comprise a flasher ora knockout pot. The separator 110 may operate at a temperature from 20°C. to 350° C., e.g., from 30° C. to 325° C. or from 60° C. to 250° C.The pressure of separator 110 may be from 100 kPa to 3000 kPa, e.g.,from 125 kPa to 2500 kPa or from 150 kPa to 2200 kPa. Optionally, thecrude ethanol product in line 109 may pass through one or more membranesto separate hydrogen and/or other non-condensable gases.

The vapor stream 111 exiting separator 110 may comprise hydrogen andhydrocarbons, and may be purged and/or returned to reaction zone 101.When returned to reaction zone 101, vapor stream 110 is combined withthe hydrogen feed 104 and co-fed to vaporizer 106. In some embodiments,the returned vapor stream 111 may be compressed before being combinedwith hydrogen feed 104.

In FIG. 1, the liquid stream 112 from separator 110 is withdrawn andpumped to the side of first column 120, also referred to as an “acidseparation column.” In one embodiment, the contents of liquid stream 112are substantially similar to the crude ethanol product obtained from thereactor, except that the composition has been depleted of hydrogen,carbon dioxide, methane and/or ethane, which are removed by separator110. Accordingly, liquid stream 112 may also be referred to as a crudeethanol product. Exemplary components of liquid stream 112 are providedin Table 2. It should be understood that liquid stream 112 may containother components, not listed in Table 2.

TABLE 2 COLUMN FEED COMPOSITION (Liquid Stream 112) Conc. (wt. %) Conc.(wt. %) Conc. (wt. %) Ethanol 5 to 72 10 to 70  15 to 65 Acetic Acid <900 to 50  0 to 35 Water 5 to 50 5 to 45 10 to 40 Ethyl Acetate <30 1 to25  3 to 20 Acetaldehyde <10 0.001 to 3    0.1 to 3   Acetal <5 0.01 to5    0.01 to 3   Acetone <5 0.0005 to 0.05   0.001 to 0.03  Other Esters<5 <0.005 <0.001 Other Ethers <5 <0.005 <0.001 Other Alcohols <5 <0.005<0.001

The lower amounts indicated as less than (<) in the tables throughoutthe present specification are preferably not present and if present maybe present in trace amounts or in amounts greater than 0.0001 wt. %.

The “other esters” in Table 2 may include, but are not limited to, ethylpropionate, methyl acetate, isopropyl acetate, n-propyl acetate, n-butylacetate or mixtures thereof. The “other ethers” in Table 2 may include,but are not limited to, diethyl ether, methyl ethyl ether, isobutylethyl ether or mixtures thereof. The “other alcohols” in Table 2 mayinclude, but are not limited to, methanol, isopropanol, n-propanol,n-butanol, 2-butanol or mixtures thereof. In one embodiment, the liquidstream 112 may comprise propanol, e.g., isopropanol and/or n-propanol,in an amount from 0.001 to 0.1 wt. %, from 0.001 to 0.05 wt. % or from0.001 to 0.03 wt. %. In should be understood that these other componentsmay be carried through in any of the distillate or residue streamsdescribed herein and will not be further described herein, unlessindicated otherwise.

Optionally, crude ethanol product in line 109 or in liquid stream 112may be further fed to an esterification reactor, hydrogenolysis reactor,or combination thereof. An esterification reactor may be used to consumeresidual acetic acid present in the crude ethanol product to furtherreduce the amount of acetic acid that would otherwise need to beremoved. Hydrogenolysis may be used to convert ethyl acetate in thecrude ethanol product to ethanol.

In the embodiment shown in FIG. 1, line 112 is introduced in the lowerpart of first column 120, e.g., lower half or lower third. In firstcolumn 120, unreacted acetic acid, a portion of the water, and otherheavy components, if present, are removed from the composition in line121 and are withdrawn, preferably continuously, as residue. Some or allof the residue may be returned and/or recycled back to reaction zone 101via line 121. Recycling the acetic acid in line 121 to the vaporizer 106may reduce the amount of heavies that need to be purged from vaporizer106. Optionally, at least a portion of residue in line 121 may be purgedfrom the system. Reducing the amount of heavies to be purged may improveefficiencies of the process while reducing byproducts.

First column 120 also forms an overhead distillate, which is withdrawnin line 122, and which may be condensed and refluxed, for example, at aratio from 10:1 to 1:10, e.g., from 3:1 to 1:3 or from 1:2 to 2:1.

When column 120 is operated under standard atmospheric pressure, thetemperature of the residue exiting in line 121 preferably is from 95° C.to 120° C., e.g., from 110° C. to 117° C. or from 111° C. to 115° C. Thetemperature of the distillate exiting in line 122 preferably is from 70°C. to 110° C., e.g., from 75° C. to 95° C. or from 80° C. to 90° C.Column 120 preferably operates at ambient pressure. In otherembodiments, the pressure of first column 120 may range from 0.1 kPa to510 kPa, e.g., from 1 kPa to 475 kPa or from 1 kPa to 375 kPa.

Exemplary components of the distillate and residue compositions forfirst column 120 are provided in Table 3 below. It should also beunderstood that the distillate and residue may also contain othercomponents, not listed, such as components in the feed. For convenience,the distillate and residue of the first column may also be referred toas the “first distillate” or “first residue.” The distillates orresidues of the other columns may also be referred to with similarnumeric modifiers (second, third, etc.) in order to distinguish themfrom one another, but such modifiers should not be construed asrequiring any particular separation order.

TABLE 3 ACID COLUMN 120 (FIG. 1) Conc. (wt. %) Conc. (wt. %) Conc. (wt.%) Distillate Ethanol 20 to 75 30 to 70 40 to 65 Water 10 to 40 15 to 3520 to 35 Acetic Acid <2 0.001 to 0.5  0.01 to 0.2  Ethyl Acetate <60 5.0to 40  10 to 30 Acetaldehyde <10 0.001 to 5    0.01 to 4   Acetal <0.1<0.1 <0.05 Acetone <0.05 0.001 to 0.03   0.01 to 0.025 Residue AceticAcid  60 to 100 70 to 95 85 to 92 Water <30  1 to 20  1 to 15 Ethanol <1<0.9 <0.07

As shown in Table 3, without being bound by theory, it has surprisinglyand unexpectedly been discovered that when any amount of acetal isdetected in the feed that is introduced to the acid separation column120, the acetal appears to decompose in the column such that less oreven no detectable amounts are present in the distillate and/or residue.

The distillate in line 122 preferably comprises ethanol, ethyl acetate,and water, along with other impurities, which may be difficult toseparate due to the formation of binary and tertiary azeotropes. Tofurther separate distillate, line 122 is introduced to the second column123, also referred to as the “light ends column,” preferably in themiddle part of column 123, e.g., middle half or middle third. Preferablythe second column 123 is an extractive distillation column, and anextraction agent is added thereto.

Extractive distillation is a method of separating close boilingcomponents, such as azeotropes, by distilling the feed in the presenceof an extraction agent. The extraction agent preferably has a boilingpoint that is higher than the compounds being separated in the feed. Inpreferred embodiments, the extraction agent is comprised primarily ofwater. As indicated above, the first distillate in line 122 that is fedto the second column 123 comprises ethyl acetate, ethanol, and water.These compounds tend to form binary and ternary azeotropes, whichdecrease separation efficiency

The molar ratio of the water in the extraction agent to the ethanol inthe feed to the second column is preferably at least 0.5:1, e.g., atleast 1:1 or at least 3:1. In terms of ranges, preferred molar ratiosmay range from 0.5:1 to 8:1, e.g., from 1:1 to 7:1 or from 2:1 to 6.5:1.Higher molar ratios may be used but with diminishing returns in terms ofthe additional ethyl acetate in the second distillate and decreasedethanol concentrations in the second column distillate.

In one embodiment, an additional extraction agent, such as water from anexternal source, dimethylsulfoxide, glycerine, diethylene glycol,1-naphthol, hydroquinone, N,N′-dimethylformamide, 1,4-butanediol;ethylene glycol-1,5-pentanediol; propylene glycol-tetraethyleneglycol-polyethylene glycol; glycerine-propylene glycol-tetraethyleneglycol-1,4-butanediol, ethyl ether, methyl formate, cyclohexane,N,N′-dimethyl-1,3-propanediamine, N,N′-dimethylethylenediamine,diethylene triamine, hexamethylene diamine and 1,3-diaminopentane, analkylated thiopene, dodecane, tridecane, tetradecane and chlorinatedparaffins, may be added to second column 123. Some suitable extractionagents include those described in U.S. Pat. Nos. 4,379,028, 4,569,726,5,993,610 and 6,375,807, the entire contents and disclosure of which arehereby incorporated by reference. The additional extraction agent may becombined with the recycled third residue in line 124 and co-fed to thesecond column 123. The additional extraction agent may also be addedseparately to the second column 123. In one aspect, the extraction agentcomprises an extraction agent, e.g., water, derived from an externalsource via line 125 and none of the extraction agent is derived from thethird residue.

Second column 123 may be a tray or packed column. In one embodiment,second column 123 is a tray column having from 5 to 70 trays, e.g., from15 to 50 trays or from 20 to 45 trays. Although the temperature andpressure of second column 123 may vary, when at atmospheric pressure thetemperature of the second residue exiting in line 126 preferably is from60° C. to 90° C., e.g., from 70° C. to 90° C. or from 80° C. to 90° C.The temperature of the second distillate exiting in line 127 from secondcolumn 123 preferably is from 50° C. to 90° C., e.g., from 60° C. to 80°C. or from 60° C. to 70° C. Column 123 may operate at atmosphericpressure. In other embodiments, the pressure of second column 123 mayrange from 0.1 kPa to 510 kPa, e.g., from 1 kPa to 475 kPa or from 1 kPato 375 kPa. Exemplary components for the distillate and residuecompositions for second column 123 are provided in Table 4 below. Itshould be understood that the distillate and residue may also containother components, not listed, such as components in the feed.

TABLE 4 SECOND COLUMN 123 (FIG. 1) Conc. (wt. %) Conc. (wt. %) Conc.(wt. %) Distillate Ethyl Acetate 10 to 99 25 to 95 50 to 93 Acetaldehyde<25 0.5 to 15  1 to 8 Water <25 0.5 to 20   4 to 16 Ethanol <30 0.001 to15   0.01 to 5   Acetal <5 0.001 to 2    0.01 to 1   Residue Water 30 to90 40 to 85 50 to 85 Ethanol 10 to 75 15 to 60 20 to 50 Ethyl Acetate <30.001 to 2    0.001 to 0.5  Acetic Acid <0.5 0.001 to 0.3  0.001 to 0.2 

In preferred embodiments, the recycling of the third residue promotesthe separation of ethyl acetate from the residue of the second column123. For example, the weight ratio of ethyl acetate in the secondresidue to second distillate preferably is less than 0.4:1, e.g., lessthan 0.2:1 or less than 0.1:1. In embodiments that use an extractivedistillation column with water as an extraction agent as the secondcolumn 123, the weight ratio of ethyl acetate in the second residue toethyl acetate in the second distillate approaches zero. Second residuemay comprise, for example, from 30% to 99.5% of the water and from 85 to100% of the acetic acid from line 122. The second distillate in line 127comprises ethyl acetate and additionally comprises water, ethanol,and/or acetaldehyde. Second distillate 127 may be substantially free ofacetic acid. In an optional embodiment, a portion of the seconddistillate in line 127′ may be combined with line 132 discussed belowand fed to vaporizer 106. Also depending on the water concentration ofthe second distillate in line 127′ an optional water stream in line 106may be necessary to promote the activity of the catalyst to convertethyl acetate.

The weight ratio of ethanol in the second residue to second distillatepreferably is at least 3:1, e.g., at least 6:1, at least 8:1, at least10:1 or at least 15:1. All or a portion of the third residue is recycledto the second column. In one embodiment, all of the third residue may berecycled until process 100 reaches a steady state and then a portion ofthe third residue is recycled with the remaining portion being purgedfrom the system 100. The composition of the second residue will tend tohave lower amounts of ethanol than when the third residue is notrecycled. As the third residue is recycled, the composition of thesecond residue, as provided in Table 4, comprises less than 30 wt. % ofethanol, e.g., less than 20 wt. % or less than 15 wt. %. The majority ofthe second residue preferably comprises water. Notwithstanding thiseffect, the extractive distillation step advantageously also reduces theamount of ethyl acetate that is sent to the third column, which ishighly beneficial in ultimately forming a highly pure ethanol product.

As shown, the second residue from second column 123, which comprisesethanol and water, is fed via line 126 to third column 128, alsoreferred to as the “product column.” More preferably, the second residuein line 126 is introduced in the lower part of third column 128, e.g.,lower half or lower third. Third column 128 recovers ethanol, whichpreferably is substantially pure with respect to organic impurities andother than the azeotropic water content, as the distillate in line 129.The distillate of third column 128 preferably is refluxed as shown inFIG. 1, for example, at a reflux ratio from 1:10 to 10:1, e.g., from 1:3to 3:1 or from 1:2 to 2:1. In one embodiment (not shown), a firstportion of the third residue in line 130 is recycled to the secondcolumn and a second portion is purged and removed from the system. Inone embodiment, once the process reaches steady state, the secondportion of water to be purged is substantially similar to the amountwater formed in the hydrogenation of acetic acid. In one embodiment, aportion of the third residue may be used to hydrolyze any other stream,such as one or more streams comprising ethyl acetate.

Third column 128 is preferably a tray column as described above andoperates at atmospheric pressure or optionally at pressures above orbelow atmospheric pressure. The temperature of the third distillateexiting in line 129 preferably is from 60° C. to 110° C., e.g., from 70°C. to 100° C. or from 75° C. to 95° C. The temperature of the thirdresidue in line 130 preferably is from 70° C. to 115° C., e.g., from 80°C. to 110° C. or from 85° C. to 105° C. Exemplary components of thedistillate and residue compositions for third column 128 are provided inTable below. It should be understood that the distillate and residue mayalso contain other components, not listed, such as components in thefeed.

TABLE 5 THIRD COLUMN 128 (FIG. 1) Conc. (wt. %) Conc. (wt. %) Conc. (wt.%) Distillate Ethanol 75 to 96  80 to 96 85 to 96 Water <12 1 to 9 3 to8 Acetic Acid <12 0.0001 to 0.1   0.005 to 0.05  Ethyl Acetate <120.0001 to 0.05  0.005 to 0.025 Acetaldehyde <12 0.0001 to 0.1   0.005 to0.05  Diethyl Acetal <12 0.0001 to 0.05  0.005 to 0.025 Residue Water 75to 100  80 to 100  90 to 100 Ethanol <0.8 0.001 to 0.5  0.005 to 0.05 Ethyl Acetate <1 0.001 to 0.5  0.005 to 0.2  Acetic Acid <2 0.001 to0.5  0.05 0.2 

Any of the compounds that are carried through the distillation processfrom the feed or crude reaction product generally remain in the thirddistillate in amounts of less 0.1 wt. %, based on the total weight ofthe third distillate composition, e.g., less than 0.05 wt. % or lessthan 0.02 wt. %. In one embodiment, one or more side streams may removeimpurities from any of the columns in the system 100. Preferably atleast one side stream is used to remove impurities from the third column128. The impurities may be purged and/or retained within the system 100.

The third distillate in line 129 may be further purified to form ananhydrous ethanol product stream, i.e., “finished anhydrous ethanol,”using one or more additional separation systems, such as, for example,distillation columns, adsorption units, membranes, or molecular sieves.Suitable adsorption units include pressure swing adsorption units andthermal swing adsorption unit.

Returning to second column 123, the second distillate preferably isrefluxed as shown in FIG. 1, optionally at a reflux ratio of 1:10 to10:1, e.g., from 1:5 to 5:1 or from 1:3 to 3:1. The second distillate inline 127 may be purged or recycled to the reaction zone. In oneembodiment, the second distillate in line 127 is further processed in afourth column 131, also referred to as the “acetaldehyde removalcolumn.” In fourth column 131 the second distillate is separated into afourth distillate, which comprises acetaldehyde, in line 132 and afourth residue, which comprises ethyl acetate, in line 133. The fourthdistillate preferably is refluxed at a reflux ratio from 1:20 to 20:1,e.g., from 1:15 to 15:1 or from 1:10 to 10:1, and a portion of thefourth distillate is returned to the reaction zone 101. For example, thefourth distillate may be combined with the acetic acid feed, added tothe vaporizer 106, or added directly to the reactor 108. The fourthdistillate preferably is co-fed with the acetic acid in feed line 105 tovaporizer 106. Also depending on the water concentration of the fourthdistillate in line 132 an optional water stream in line 116 may benecessary to promote the activity of the catalyst to convert ethylacetate.

Without being bound by theory, since acetaldehyde may be hydrogenated toform ethanol, the recycling of a stream that contains acetaldehyde tothe reaction zone increases the yield of ethanol and decreases byproductand waste generation. In another embodiment, the acetaldehyde may becollected and utilized, with or without further purification, to makeuseful products including but not limited to n-butanol, 1,3-butanediol,and/or crotonaldehyde and derivatives.

The fourth residue of fourth column 131 may be purged via line 133. Thefourth residue primarily comprises ethyl acetate and ethanol, which maybe suitable for use as a solvent mixture or in the production of esters.In one preferred embodiment, the acetaldehyde is removed from the seconddistillate in fourth column 131 such that no detectable amount ofacetaldehyde is present in the residue of column 131.

Fourth column 131 is preferably a tray column as described above andpreferably operates above atmospheric pressure. In one embodiment, thepressure is from 120 kPa to 5,000 kPa, e.g., from 200 kPa to 4,500 kPa,or from 400 kPa to 3,000 kPa. In a preferred embodiment the fourthcolumn 131 may operate at a pressure that is higher than the pressure ofthe other columns.

The temperature of the fourth distillate exiting in line 132 preferablyis from 60° C. to 110° C., e.g., from 70° C. to 100° C. or from 75° C.to 95° C. The temperature of the residue in line 133 preferably is from70° C. to 115° C., e.g., from 80° C. to 110° C. or from 85° C. to 110°C. Exemplary components of the distillate and residue compositions forfourth column 131 are provided in Table 6 below. It should be understoodthat the distillate and residue may also contain other components, notlisted, such as components in the feed.

TABLE 6 FOURTH COLUMN 131 (FIG. 1) Conc. (wt. %) Conc. (wt. %) Conc.(wt. %) Distillate Acetaldehyde 2 to 80    2 to 50   5 to 40 EthylAcetate <90   30 to 80   40 to 75 Ethanol <30 0.001 to 25 0.01 to 20Water <25 0.001 to 20 0.01 to 15 Residue Ethyl Acetate 40 to 100    50to 100  60 to 100 Ethanol <40 0.001 to 30 0.01 to 15 Water <25 0.001 to20   2 to 15 Acetaldehyde <1  0.001 to 0.5 Not detectable Acetal <30.001 to 2  0.01 to 1 

In one embodiment, a portion of the third residue in line 124 isrecycled to second column 123. In one embodiment, recycling the thirdresidue further reduces the aldehyde components in the second residueand concentrates these aldehyde components in second distillate in line127 and thereby sent to the fourth column 131, wherein the aldehydes maybe more easily separated. The third distillate in line 129 may havelower concentrations of aldehydes and esters due to the recycling ofthird residue in line 124.

FIG. 2 illustrates another exemplary separation system. The reactionzone 101 of FIG. 2 is similar to FIG. 1 and produces a liquid stream112, e.g., crude ethanol product, for further separation. In onepreferred embodiment, the reaction zone 101 of FIG. 2 operates at above80% acetic acid conversion, e.g., above 90% conversion or above 99%conversion. Thus, the acetic acid concentration in the liquid stream 112may be low.

Liquid stream 112 is introduced in the middle or lower portion of afirst column 150, also referred to as acid-water column. For purposes ofconvenience, the columns in each exemplary separation process, may bereferred as the first, second, third, etc., columns, but it isunderstood that first column 150 in FIG. 2 operates differently than thefirst column 120 of FIG. 1. In one embodiment, no entrainers are addedto first column 150. In FIG. 2, first column 150, water and unreactedacetic acid, along with any other heavy components, if present, areremoved from liquid stream 112 and are withdrawn, preferablycontinuously, as a first residue in line 151. Preferably, a substantialportion of the water in the crude ethanol product that is fed to firstcolumn 150 may be removed in the first residue, for example, up to about75% or to about 90% of the water from the crude ethanol product. Firstcolumn 150 also forms a first distillate, which is withdrawn in line152.

When column 150 is operated under about 170 kPa, the temperature of theresidue exiting in line 151 preferably is from 90° C. to 130° C., e.g.,from 95° C. to 120° C. or from 100° C. to 115° C. The temperature of thedistillate exiting in line 152 preferably is from 60° C. to 90° C.,e.g., from 65° C. to 85° C. or from 70° C. to 80° C. In someembodiments, the pressure of first column 150 may range from 0.1 kPa to510 kPa, e.g., from 1 kPa to 475 kPa or from 1 kPa to 375 kPa.

The first distillate in line 152 comprises water, in addition to ethanoland other organics. In terms of ranges, the concentration of water inthe first distillate in line 152 preferably less than 20 wt. %, e.g.,from 1 wt. % to 19 wt. % or from 5 wt. % to 15 wt. %. A portion of firstdistillate in line 153 may be condensed and refluxed, for example, at aratio from 10:1 to 1:10, e.g., from 3:1 to 1:3 or from 1:2 to 2:1. It isunderstood that reflux ratios may vary with the number of stages, feedlocations, column efficiency and/or feed composition. Operating with areflux ratio of greater than 3:1 may be less preferred because moreenergy may be required to operate the first column 150. The condensedportion of the first distillate may also be fed to a second column 154.

The remaining portion of the first distillate in 152 is fed to a waterseparation unit 156. Water separation unit 156 may be an adsorptionunit, membrane, molecular sieves, extractive column distillation, or acombination thereof. A membrane or an array of membranes may also beemployed to separate water from the distillate. The membrane or array ofmembranes may be selected from any suitable membrane that is capable ofremoving a permeate water stream from a stream that also comprisesethanol and ethyl acetate.

In a preferred embodiment, water separator 156 is a pressure swingadsorption (PSA) unit. The PSA unit is optionally operated at atemperature from 30° C. to 160° C., e.g., from 80° C. to 140° C., and apressure from 0.01 kPa to 550 kPa, e.g., from 1 kPa to 150 kPa. The PSAunit may comprise two to five beds. Water separator 156 may remove waterin an amount necessary for the ethanol product, which may vary. Forhydrous ethanol application, water separator 156 may remove water in anamount greater than 10% from the portion of first distillate in line152, e.g., greater than 20% or greater than 35%. For anhydrous ethanolapplications, water separator 156 may remove at least 95% of the waterfrom the portion of first distillate in line 152, and more preferablyfrom 95% to 99.99% of the water from the first distillate, in a waterstream 157. All or a portion of water stream 157 may be returned tocolumn 150 in line 158, where the water preferably is ultimatelyrecovered from column 150 in the first residue in line 151. Additionallyor alternatively, all or a portion of water stream 157 may be purged vialine 159. The remaining portion of first distillate exits the waterseparator 156 as ethanol mixture stream 160. Ethanol mixture stream 160may have a low concentration of water of less than 10 wt. %, e.g., lessthan 6 wt. % or less than 2 wt. %. Exemplary components of ethanolmixture stream 160 and first residue in line 151 are provided in Table 7below. It should also be understood that these streams may also containother components, not listed, such as components derived from the feed.

TABLE 7 FIRST COLUMN 150 WITH PSA (FIG. 2) Conc. (wt. %) Conc. (wt. %)Conc. (wt. %) Ethanol Mixture Stream Ethanol 20 to 95  30 to 95 40 to 95Water <10 0.01 to 6   0.1 to 2   Acetic Acid <2 0.001 to 0.5  0.01 to0.2  Ethyl Acetate <60  1 to 55  5 to 55 Acetaldehyde <10 0.001 to 5   0.01 to 4   Acetal <0.1 <0.1 <0.05 Acetone <0.05 0.001 to 0.03   0.01 to0.025 Residue Acetic Acid <90  1 to 50  2 to 35 Water 30 to 100 45 to 9560 to 90 Ethanol <1 <0.9 <0.3

Preferably, ethanol mixture stream 160 is not returned or refluxed tofirst column 150. The condensed portion of the first distillate in line153 may be combined with ethanol mixture stream 160 to control the waterconcentration fed to the second column 154. For example, in someembodiments the first distillate may be split into equal portions, whilein other embodiments, all of the first distillate may be condensed orall of the first distillate may be processed in the water separationunit. In FIG. 2, the condensed portion in line 153 and ethanol mixturestream 160 are co-fed to second column 154. In other embodiments, thecondensed portion in line 153 and ethanol mixture stream 160 may beseparately fed to second column 154. The combined distillate and ethanolmixture has a total water concentration of greater than 0.5 wt. %, e.g.,greater than 2 wt. % or greater than 5 wt. %. In terms of ranges, thetotal water concentration of the combined distillate and ethanol mixturemay be from 0.5 to 15 wt. %, e.g., from 2 to 12 wt. %, or from 5 to 10wt. %.

The second column 154 in FIG. 2, also referred to as the “light endscolumn,” removes ethyl acetate and acetaldehyde from the firstdistillate in line 153 and/or ethanol mixture stream 160. Ethyl acetateand acetaldehyde are removed as a second distillate in line 161 andethanol is removed as the second residue in line 162. Second column 108may be a tray column or packed column. In one embodiment, second column154 is a tray column having from 5 to 70 trays, e.g., from 15 to 50trays or from 20 to 45 trays.

Second column 154 operates at a pressure ranging from 0.1 kPa to 510kPa, e.g., from 10 kPa to 450 kPa or from 50 kPa to 350 kPa. Althoughthe temperature of second column 154 may vary, when at about 20 kPa to70 kPa, the temperature of the second residue exiting in line 162preferably is from 30° C. to 75° C., e.g., from 35° C. to 70° C. or from40° C. to 65° C. The temperature of the second distillate exiting inline 161 preferably is from 20° C. to 55° C., e.g., from 25° C. to 50°C. or from 30° C. to 45° C.

The total concentration of water fed to second column 154 preferably isless than 10 wt. %, as discussed above. When first distillate in line153 and/or ethanol mixture stream comprises minor amounts of water,e.g., less than 1 wt. % or less than 0.5 wt. %, additional water may befed to the second column 154 as an extractive agent in the upper portionof the column. A sufficient amount of water is preferably added via theextractive agent such that the total concentration of water fed tosecond column 154 is from 1 to 10 wt. % water, e.g., from 2 to 6 wt. %,based on the total weight of all components fed to second column 154. Ifthe extractive agent comprises water, the water may be obtained from anexternal source or from an internal return/recycle line from one or moreof the other columns or water separators.

Suitable extractive agents may also include, for example,dimethylsulfoxide, glycerine, diethylene glycol, 1-naphthol,hydroquinone, N,N′-dimethylformamide, 1,4-butanediol; ethyleneglycol-1,5-pentanediol; propylene glycol-tetraethyleneglycol-polyethylene glycol; glycerine-propylene glycol-tetraethyleneglycol-1,4-butanediol, ethyl ether, methyl formate, cyclohexane,N,N′-dimethyl-1,3-propanediamine, N,N′-dimethylethylenediamine,diethylene triamine, hexamethylene diamine and 1,3-diaminopentane, analkylated thiopene, dodecane, tridecane, tetradecane, chlorinatedparaffins, or a combination thereof. When extractive agents are used, asuitable recovery system, such as a further distillation column, may beused to recycle the extractive agent.

Exemplary components for the second distillate and second residuecompositions for the second column 154 are provided in Table 8, below.It should be understood that the distillate and residue may also containother components, not listed in Table 8.

TABLE 8 SECOND COLUMN 154 (FIG. 2) Conc. (wt. %) Conc. (wt. %) Conc.(wt. %) Second Distillate Ethyl Acetate 5 to 90  10 to 80 15 to 75Acetaldehyde <60  1 to 40  1 to 35 Ethanol <45 0.001 to 40   0.01 to35   Water <20 0.01 to 10   0.1 to 5   Second Residue Ethanol 80 to 99.585 to 97 60 to 95 Water <20 0.001 to 15   0.01 to 10   Ethyl Acetate <10.001 to 2    0.001 to 0.5  Acetic Acid <0.5 <0.01 0.001 to 0.01 

The second residue in FIG. 2 comprises one or more impurities selectedfrom the group consisting of ethyl acetate, acetic acid, acetaldehyde,and diethyl acetal. The second residue may comprise at least 100 wppm ofthese impurities, e.g., at least 250 wppm or at least 500 wppm. In someembodiments, the second residue may contain substantially no ethylacetate or acetaldehyde.

The second distillate in line 161, which comprises ethyl acetate and/oracetaldehyde, preferably is refluxed as shown in FIG. 2, for example, ata reflux ratio from 1:30 to 30:1, e.g., from 1:10 to 10:1 or from 1:3 to3:1. In one aspect, not shown, the second distillate 161 or a portionthereof may be returned to reactor 108. The ethyl acetate and/oracetaldehyde in the second distillate may be further reacted inhydrogenation reactor 108. Also depending on the water concentration ofthe second distillate in line 161 an optional water stream in line 116may be necessary to promote the activity of the catalyst to convertethyl acetate.

In one embodiment, the second distillate in line 161 and/or a refinedsecond distillate, or a portion of either or both streams, may befurther separated to produce an acetaldehyde-containing stream and anethyl acetate-containing stream. This may allow a portion of either theresulting acetaldehyde-containing stream or ethyl acetate-containingstream to be recycled to reactor 108 while purging the other stream. Thepurge stream may be valuable as a source of either ethyl acetate and/oracetaldehyde.

FIG. 3 illustrates another exemplary separation system. The reactionzone 101 of FIG. 3 is similar to FIG. 1 and produces a liquid stream112, e.g., crude ethanol product, for further separation. In onepreferred embodiment, the reaction zone 101 of FIG. 3 operates at above80% acetic acid conversion, e.g., above 90% conversion or above 99%conversion. Thus, the acetic acid concentration in the liquid stream 112may be low.

In addition to liquid stream 113, an optional extractive agent (notshown) and an optional ethyl acetate recycle stream in line 179 may alsobe fed to first column 170. The optional extractive agent may comprisewater that is introduced above the feed location of the liquid stream112. In some embodiment, the optional extractive agent may be a diluteacid stream comprising up to 20 wt. % acetic acid. Also, the optionalethyl acetate recycle stream may have a relatively high ethanolconcentration, e.g. from 70 to 90 wt. %, and may be fed above or nearthe feed point of the liquid stream 112. In one embodiment, first column170 is a tray column having from 5 to 90 theoretical trays, e.g. from 10to 60 theoretical trays or from 15 to 50 theoretical trays. The numberof actual trays for each column may vary depending on the trayefficiency, which is typically from 0.5 to 0.7 depending on the type oftray. The trays may be sieve trays, fixed valve trays, movable valvetrays, or any other suitable design known in the art. In otherembodiments, a packed column having structured packing or random packingmay be employed.

When first column 170 is operated under 50 kPa, the temperature of theresidue exiting in line 171 preferably is from 20° C. to 100° C., e.g.,from 30° C. to 90° C. or from 40° C. to 80° C. The base of column 170may be maintained at a relatively low temperature by withdrawing aresidue stream comprising ethanol, ethyl acetate, water, and aceticacid, thereby providing an energy efficiency advantage. The temperatureof the distillate exiting in line 172 preferably at 50 kPa is from 10°C. to 80° C., e.g., from 20° C. to 70° C. or from 30° C. to 60° C. Thepressure of first column 170 may range from 0.1 kPa to 510 kPa, e.g.,from 1 kPa to 475 kPa or from 1 kPa to 375 kPa. In some embodiments,first column 170 may operate under a vacuum of less than 70 kPa, e.g.,less than 50 kPa, or less than 20 kPa. Operating under a vacuum maydecrease the reboiler duty and reflux ratio of first column 170.However, a decrease in operating pressure for first column 170 does notsubstantially affect column diameter.

In first column 170, a weight majority of the ethanol, water, aceticacid, are removed from the organic feed, including liquid stream 112 andthe optional ethyl acetate recycle stream in line 179, and arewithdrawn, preferably continuously, as residue in line 171. Thisincludes any water added as the optional extractive agent. Concentratingthe ethanol in the residue reduces the amount of ethanol that isrecycled to reactor 108 and in turn reduces the size of reactor 108.Preferably less than 10% of the ethanol from the organic feed, e.g.,less than 5% or less than 1% of the ethanol, is returned to reactor 108from first column 170. In addition, concentrating the ethanol also willconcentrate the water and/or acetic acid in the residue. In oneembodiment, at least 90% of the ethanol from the organic feed iswithdrawn in the residue, and more preferably at least 95%. In addition,ethyl acetate may also be present in the first residue in line 171. Thereboiler duty may decrease with an ethyl acetate concentration increasein the first residue in line 171.

First column 170 also forms a distillate, which is withdrawn in line172, and which may be condensed and refluxed, for example, at a ratiofrom 30:1 to 1:30, e.g., from 10:1 to 1:10 or from 5:1 to 1:5. Highermass flow ratios of water to organic feed may allow first column 170 tooperate with a reduced reflux ratio.

First distillate in line 172 preferably comprises a weight majority ofthe acetaldehyde and ethyl acetate from liquid stream 112, as well asfrom the optional ethyl acetate recycle stream in line 179. In oneembodiment, the first distillate in line 172 comprises a concentrationof ethyl acetate that is less than the ethyl acetate concentration forthe azeotrope of ethyl acetate and water, and more preferably less than75 wt. %.

In some embodiments, first distillate in stream 172 also comprisesethanol. Returning the first distillate comprising ethanol to thereactor may require an increase in reactor capacity to maintain the samelevel of ethanol efficiency. In one embodiment, it is preferred toreturn to the reactor less than 10% of the ethanol from the crudeethanol stream, e.g., less than 5% or less than 1%. In terms of ranges,the amount of returned ethanol is from 0.01 to 10% of the ethanol in thecrude ethanol stream, e.g. from 0.1 to 5% or from 0.2 to 1%. In oneembodiment, to reduce the amount of ethanol returned, the ethanol may berecovered from the first distillate in line 172 using an optionalextractor or extractive distillation column.

Exemplary components of the distillate and residue compositions forfirst column 170 are provided in Table 9 below. It should also beunderstood that the distillate and residue may also contain othercomponents, not listed in Table 9. For convenience, the distillate andresidue of the first column may also be referred to as the “firstdistillate” or “first residue.” The distillates or residues of the othercolumns may also be referred to with similar numeric modifiers (second,third, etc.) in order to distinguish them from one another, but suchmodifiers should not be construed as requiring any particular separationorder.

TABLE 9 FIRST COLUMN 170 (FIG. 3) Conc. (wt. %) Conc. (wt. %) Conc. (wt.%) Distillate Ethyl Acetate 10 to 85 15 to 80 20 to 75 Acetaldehyde 0.1to 70  0.2 to 65  0.5 to 65 Acetal <0.1 <0.1 <0.05 Acetone <0.05 0.001to 0.03   0.01 to 0.025 Ethanol  3 to 55  4 to 50  5 to 45 Water 0.1 to20   1 to 15  2 to 10 Acetic Acid <2 <0.1 <0.05 Residue Acetic Acid 0.01to 35   0.1 to 30  0.2 to 25  Water  5 to 40 10 to 35 15 to 30 Ethanol10 to 75 15 to 70 20 o 65

In one embodiment of the present invention, first column 170 may beoperated at a temperature where most of the water, ethanol, and aceticacid are removed into the residue stream and only a small amount ofethanol and water is collected in the distillate stream due to theformation of binary and tertiary azeotropes. The weight ratio of waterin the residue in line 171 to water in the distillate in line 172 may begreater than 1:1, e.g., greater than 2:1. There may be more water inresidue in line 171 when an optional extractive agent is used. Theweight ratio of ethanol in the residue to ethanol in the distillate maybe greater than 1:1, e.g., greater than 2:1

The amount of acetic acid in the first residue may vary dependingprimarily on the conversion in reactor 108. In one embodiment, when theconversion is high, e.g., greater than 90%, the amount of acetic acid inthe first residue may be less than 10 wt. %, e.g., less than 5 wt. % orless than 2 wt. %. In other embodiments, when the conversion is lower,e.g., less than 90%, the amount of acetic acid in the first residue maybe greater than 10 wt. %.

The distillate preferably is substantially free of acetic acid, e.g.,comprising less than 1000 ppm, less than 500 ppm or less than 100 ppmacetic acid. The distillate may be purged from the system or recycled inwhole or part to reactor 108. In some embodiments, the distillate may befurther separated, e.g., in a distillation column (not shown), into anacetaldehyde stream and an ethyl acetate stream. Either of these streamsmay be returned to reactor 108 or separated from system 100 asadditional products. The ethyl acetate stream may also be hydrolyzed orreduced with hydrogen, via hydrogenolysis, to produce ethanol. Whenadditional ethanol is produced, it is preferred that the additionalethanol is recovered and not directed to reactor 108.

Some species, such as acetals, may decompose in first column 170 suchthat very low amounts, or even no detectable amounts, of acetals remainin the distillate or residue.

To recover ethanol, first residue in line 171 may be further separated,depending on the concentration of acetic acid and/or ethyl acetate

In FIG. 3, residue in line 171 is further separated in a second column173, also referred to as an “acid separation column.” Second column 173yields a second residue in line 174 comprising acetic acid and water,and a second distillate in line 175 comprising ethanol and ethylacetate. In one embodiment, a weight majority of the water and/or aceticacid fed to second column 173 is removed in the second residue in line174, e.g., at least 60% of the water and/or acetic acid is removed inthe second residue in line 174 or more preferably at least 80% of thewater and/or acetic acid. An acid column may be desirable, for example,when the acetic acid concentration in the first residue is greater 50wppm, e.g., greater than 0.1 wt. %, greater than 1 wt. %, e.g., greaterthan 5 wt. %.

In one embodiment, a portion of the first residue in line 171 may bepreheated prior to being introduced into second column 173, as shown inFIG. 3. After preheating first residue in line 171 may be converted intoa partial vapor feed having less than 30 mol. % of the contents in thevapor phase, e.g., less than 25 mol. % or less than 20 mol. %. In termsof ranges, from 1 to 30 mol. % is in the vapor phase, e.g., from 5 to 20mol. %. Greater vapor phase contents result in increased energyconsumption and a significant increase in the size of second column 173.

Second column 173 operates in a manner to concentrate the ethanol fromfirst residue so that a majority of the ethanol is carried overhead.Thus, the residue of second column 173 may have a low ethanolconcentration of less than 5 wt. %, e.g. less than 1 wt. % or less than0.5 wt. %. Lower ethanol concentrations may be achieved withoutsignificant increases in reboiler duty or column size. Thus, in someembodiments, it is efficient to reduce the ethanol concentration in theresidue to less than 50 wppm, or more preferably less than 25 wppm. Asdescribed herein, the residue of second column 173 may be treated andlower concentrations of ethanol allow the residue to be treated withoutgenerating further impurities.

In FIG. 3, the first residue in line 171 is introduced to second column173 preferably in the top part of column 173, e.g., top half or topthird. Feeding first residue in line 171 in a lower portion of secondcolumn 173 may unnecessarily increase the energy requirements. Acidcolumn 173 may be a tray column or packed column. In FIG. 3, secondcolumn 173 may be a tray column having from 10 to 110 theoretical trays,e.g. from 15 to 95 theoretical trays or from 20 to 75 theoretical trays.Additional trays may be used if necessary to further reduce the ethanolconcentration in the residue. In one embodiment, the reboiler duty andcolumn size may be reduced by increasing the number of trays.

Although the temperature and pressure of second column 173 may vary,when at atmospheric pressure the temperature of the second residue inline 174 preferably is from 95° C. to 160° C., e.g., from 100° C. to150° C. or from 110° C. to 145° C. In one embodiment, first residue inline 171 is preheated to a temperature that is within 20° C. of thetemperature of second residue in line 174, e.g., within 15° C. or within10° C. The temperature of the second distillate exiting in line 175 fromsecond column 173 preferably is from 50° C. to 120° C., e.g., from 75°C. to 118° C. or from 80° C. to 115° C. The temperature gradient may besharper in the base of second column 173.

The pressure of second column 173 may range from 0.1 kPa to 510 kPa,e.g., from 1 kPa to 475 kPa or from 1 kPa to 375 kPa. In one embodiment,second column 173 operates above atmospheric pressure, e.g., above 170kPa or above 375 kPa. Second column 173 may be constructed of a materialsuch as 316L SS, Allot 2205 or Hastelloy C, depending on the operatingpressure. The reboiler duty and column size for second column 173 remainrelatively constant until the ethanol concentration in the seconddistillate in line 175 is greater than 90 wt. %.

Second column 173 also forms an overhead, which is withdrawn, and whichmay be condensed and refluxed, for example, at a ratio from 12:1 to1:12, e.g., from 10:1 to 1:10 or from 8:1 to 1:8. The overheadpreferably comprises 85 to 92 wt. % ethanol, e.g., about 87 to 90 wt. %ethanol, with the remaining balance being water and ethyl acetate. Inone embodiment, water may be removed prior to recovering the ethanolproduct as described above in FIG. 2. In one embodiment, the overhead,prior to water removal, may comprise less than 15 wt. % water, e.g.,less than 10 wt. % water or less than 8 wt. % water. Overhead vapor maybe fed to water separator, which may be an adsorption unit, membrane,molecular sieves, extractive column distillation, or a combinationthereof.

TABLE 10 SECOND COLUMN 173 (FIG. 3) Conc. (wt. %) Conc. (wt. %) Conc.(wt. %) Second Distillate Ethanol 80 to 96   85 to 92    87 to 90 EthylAcetate <30 0.001 to 15 0.005 to 4 Acetaldehyde <20 0.001 to 15 0.005 to4 Water <20 0.001 to 10  0.01 to 8 <2 0.001 to 1    0.005 to 0.5 SecondResidue Acetic Acid Water 0.1 to 55   0.2 to 40   0.5 to 35 EthylAcetate   45 to 99.9   55 to 99.8    65 to 99.5 Ethanol <0.1  0.0001 to0.05   0.0001 to 0.01 Second Distillate <5 0.002 to 1    0.05 0.5

The weight ratio of ethanol in second distillate in line 175 to ethanolin the second residue in line 174 preferably is at least 35:1.Preferably, second distillate in line 175 is substantially free ofacetic acid and may contain, if any, trace amounts of acetic acid.

In one embodiment, ethyl acetate fed to second column 173 mayconcentrate in the second distillate in line 175. Thus, preferably noethyl acetate is withdrawn in the second residue in line 174.Advantageously this allows most of the ethyl acetate to be subsequentlyrecovered without having to further process the second residue in line174.

In one embodiment, as shown in FIG. 3, due to the presence of ethylacetate in second distillate in line 175, an additional third column 176may be used. Third column 176, referred to as a “product” column, isused for removing ethyl acetate from second distillate in line 175 andproducing an ethanol product in the third residue in line 177. Productcolumn 176 may be a tray column or packed column. In FIG. 3, thirdcolumn 176 may be a tray column having from 5 to 90 theoretical trays,e.g. from 10 to 60 theoretical trays or from 15 to 50 theoretical trays.

The feed location of second distillate in line 175 may vary depending onethyl acetate concentration and it is preferred to feed seconddistillate in line 175 to the upper portion of third column 176. Higherconcentrations of ethyl acetate may be fed at a higher location in thirdcolumn 176. The feed location should avoid the very top trays, near thereflux, to avoid excess reboiler duty requirements for the column and anincrease in column size. For example, in a column having 45 actualtrays, the feed location should between 10 to 15 trays from the top.Feeding at a point above this may increase the reboiler duty and size ofthird column 176.

Second distillate in line 175 may be fed to third column 176 at atemperature of up to 70° C., e.g., up to 50° C., or up to 40° C. In someembodiments it is not necessary to further preheat second distillate inline 175.

Ethyl acetate may be concentrated in the third distillate in line 178.Due to the relatively lower amounts of ethyl acetate fed to third column176, third distillate in line 178 also comprises substantial amounts ofethanol. To recover the ethanol, third distillate in line 178 may be fedto first column 170 as an optional ethyl acetate recycle stream 179.Depending on the ethyl acetate concentration of optional ethyl acetaterecycle stream 179 this stream may be introduced above or near the feedpoint of the liquid stream 112. Depending on the targeted ethyl acetateconcentration in the distillate of first column 172 the feed point ofoptional ethyl acetate recycle stream 179 will vary. Liquid stream 112and optional ethyl acetate recycle stream 179 collectively comprise theorganic feed to first column 170. In one embodiment, organic feedcomprises from 1 to 25% of optional ethyl acetate recycle stream 179,e.g., from 3% to 20% or from 5% to 15%. This amount may vary dependingon the production of reactor 108 and amount of ethyl acetate to berecycled.

Because optional ethyl acetate recycle stream 179 increases the demandson the first and second columns, it is preferred that the ethanolconcentration in third distillate in line 179 be from 70 to 90 wt. %,e.g., from 72 to 88 wt. %, or from 75 to 85 wt. %. In other embodiments,a portion of third distillate in line 178 may be purged from the systemas additional products, such as an ethyl acetate solvent. In addition,ethanol may be recovered from a portion of the third distillate in line178 using an extractant, such as benzene, propylene glycol, andcyclohexane, so that the raffinate comprises less ethanol to recycle.

In an optional embodiment, the third residue may be further processed torecover ethanol with a desired amount of water, for example, using afurther distillation column, adsorption unit, membrane or combinationthereof, may be used to further remove water from third residue in line177 as necessary.

Third column 176 is preferably a tray column as described above andpreferably operates at atmospheric pressure. The temperature of thethird residue in line 177 exiting from third column 176 preferably isfrom 65° C. to 110° C., e.g., from 70° C. to 100° C. or from 75° C. to80° C. The temperature of the third distillate in line 178 exiting fromthird column 176 preferably is from 30° C. to 70° C., e.g., from 40° C.to 65° C. or from 50° C. to 65° C.

The pressure of third column 176 may range from 0.1 kPa to 510 kPa,e.g., from 1 kPa to 475 kPa or from 1 kPa to 375 kPa. In someembodiments, third column 176 may operate under a vacuum of less than 70kPa, e.g., less than 50 kPa, or less than 20 kPa. Decreases in operatingpressure substantially decreases column diameter and reboiler duty forthird column 176.

Exemplary components for ethanol mixture stream and residue compositionsfor third column 176 are provided in Table 11 below. It should beunderstood that the distillate and residue may also contain othercomponents, not listed in Table 11.

TABLE 11 PRODUCT COLUMN (FIG. 3) Conc. (wt. %) Conc. (wt. %) Conc. (wt.%) Third Distillate Ethanol 70 to 99 72 to 95 75 to 90 Ethyl Acetate  1to 30  1 to 25  1 to 15 Acetaldehyde <15 0.001 to 10   0.1 to 5   Water<10 0.001 to 2    0.01 to 1   Acetal <2 0.001 to 1    0.01 to 0.5  ThirdResidue Ethanol   80 to 99.5 85 to 97 90 to 95 Water <3 0.001 to 2   0.01 to 1   Ethyl Acetate <1.5 0.0001 to 1    0.001 to 0.5  Acetic Acid<0.5 <0.01 0.0001 to 0.01 

Some of the residues withdrawn from the separation zone 102 compriseacetic acid and water. Depending on the amount of water and acetic acidcontained in the residue of first column, e.g., 120 in FIG. 1, 150 inFIG. 2, or residue of second column 173 in FIG. 3, the residue may betreated in one or more of the following processes. The following areexemplary processes for further treating the residue and it should beunderstood that any of the following may be used regardless of aceticacid concentration. When the residue comprises a majority of aceticacid, e.g., greater than 70 wt. %, the residue may be recycled to thereactor without any separation of the water. In one embodiment, theresidue may be separated into an acetic acid stream and a water streamwhen the residue comprises a majority of acetic acid, e.g., greater than50 wt. %. Acetic acid may also be recovered in some embodiments from theresidue having a lower acetic acid concentration. The residue may beseparated into the acetic acid and water streams by a distillationcolumn or one or more membranes. If a membrane or an array of membranesis employed to separate the acetic acid from the water, the membrane orarray of membranes may be selected from any suitable acid resistantmembrane that is capable of removing a permeate water stream. Theresulting acetic acid stream optionally is returned to the reactor 108.The resulting water stream may be used as an extractive agent or tohydrolyze an ester-containing stream in a hydrolysis unit.

In other embodiments, for example, where the residue comprises less than50 wt. % acetic acid, possible options include one or more of: (i)returning a portion of the residue to reactor 108, (ii) neutralizing theacetic acid, (iii) reacting the acetic acid with an alcohol, or (iv)disposing of the residue in a waste water treatment facility. It alsomay be possible to separate a residue comprising less than 50 wt. %acetic acid using a weak acid recovery distillation column to which asolvent (optionally acting as an azeotroping agent) may be added.

Exemplary solvents that may be suitable for this purpose include ethylacetate, propyl acetate, isopropyl acetate, butyl acetate, vinylacetate, diisopropyl ether, carbon disulfide, tetrahydrofuran,isopropanol, ethanol, and C₃-C₁₂ alkanes. When neutralizing the aceticacid, it is preferred that the residue comprises less than 10 wt. %acetic acid. Acetic acid may be neutralized with any suitable alkali oralkaline earth metal base, such as sodium hydroxide or potassiumhydroxide. When reacting acetic acid with an alcohol, it is preferredthat the residue comprises less than 50 wt. % acetic acid. The alcoholmay be any suitable alcohol, such as methanol, ethanol, propanol,butanol, or mixtures thereof. The reaction forms an ester that may beintegrated with other systems, such as carbonylation production or anester production process. Preferably, the alcohol comprises ethanol andthe resulting ester comprises ethyl acetate. Optionally, the resultingester may be fed to the hydrogenation reactor.

In some embodiments, when the residue comprises very minor amounts ofacetic acid, e.g., less than 5 wt. %, the residue may be disposed of toa waste water treatment facility without further processing. The organiccontent, e.g., acetic acid content, of the residue beneficially may besuitable to feed microorganisms used in a waste water treatmentfacility.

The columns shown in FIGS. 1 to 3 may comprise any distillation columncapable of performing the desired separation and/or purification. Eachcolumn preferably comprises a tray column having from 1 to 150 trays,e.g., from 10 to 100 trays, from 20 to 95 trays or from 30 to 75 trays.The trays may be sieve trays, fixed valve trays, movable valve trays, orany other suitable design known in the art. In other embodiments, apacked column may be used. For packed columns, structured packing orrandom packing may be employed. The trays or packing may be arranged inone continuous column or they may be arranged in two or more columnssuch that the vapor from the first section enters the second sectionwhile the liquid from the second section enters the first section, etc.

The associated condensers and liquid separation vessels that may beemployed with each of the distillation columns may be of anyconventional design and are simplified in the figures. Heat may besupplied to the base of each column or to a circulating bottom streamthrough a heat exchanger or reboiler. Other types of reboilers, such asinternal reboilers, may also be used. The heat that is provided to thereboilers may be derived from any heat generated during the process thatis integrated with the reboilers or from an external source such asanother heat generating chemical process or a boiler. Although onereactor and one flasher are shown in the figures, additional reactors,flashers, condensers, heating elements, and other components may be usedin various embodiments of the present invention. As will be recognizedby those skilled in the art, various condensers, pumps, compressors,reboilers, drums, valves, connectors, separation vessels, etc., normallyemployed in carrying out chemical processes may also be combined andemployed in the processes of the present invention.

The temperatures and pressures employed in the columns may vary. As apractical matter, pressures from 10 kPa to 3000 kPa will generally beemployed in these zones although in some embodiments subatmosphericpressures or superatmospheric pressures may be employed. Temperatureswithin the various zones will normally range between the boiling pointsof the composition removed as the distillate and the composition removedas the residue. As will be recognized by those skilled in the art, thetemperature at a given location in an operating distillation column isdependent on the composition of the material at that location and thepressure of column. In addition, feed rates may vary depending on thesize of the production process and, if described, may be genericallyreferred to in terms of feed weight ratios.

The ethanol product produced by the process of the present invention maybe an industrial grade ethanol comprising from 75 to 96 wt. % ethanol,e.g., from 80 to 96 wt. % or from 85 to 96 wt. % ethanol, based on thetotal weight of the ethanol product. Exemplary finished ethanolcompositional ranges are provided below in Table 12.

TABLE 12 FINISHED ETHANOL COMPOSITIONS Component Conc. (wt. %) Conc.(wt. %) Conc. (wt. %) Ethanol 85 to 99.9 90 to 99.5 92 to 99.5 Water <120.1 to 9   0.5 to 8   Acetic Acid <1 <0.1 <0.01 Ethyl Acetate <2 <0.5<0.05 Acetal <0.05 <0.01 <0.005 Acetone <0.05 <0.01 <0.005 Isopropanol<0.5 <0.1 <0.05 n-propanol <0.5 <0.1 <0.05

The finished ethanol composition of the present invention preferablycontains very low amounts, e.g., less than 0.5 wt. %, of other alcohols,such as methanol, butanol, isobutanol, isoamyl alcohol and other C₄-C₂₀alcohols. In one embodiment, the amount of isopropanol in the finishedethanol composition is from 80 to 1,000 wppm, e.g., from 95 to 1,000wppm, from 100 to 700 wppm, or from 150 to 500 wppm. In one embodiment,the finished ethanol composition is substantially free of acetaldehyde,optionally comprising less than 8 wppm acetaldehyde, e.g., less than 5wppm or less than 1 wppm. In some embodiments, when further waterseparation is used, the ethanol product may be withdrawn as a streamfrom the water separation unit as discussed above. In such embodiments,the ethanol concentration of the ethanol product may be higher thanindicated in Table 12, and preferably is greater than 97 wt. % ethanol,e.g., greater than 98 wt. % or greater than 99.5 wt. %. The ethanolproduct in this aspect preferably comprises less than 3 wt. % water,e.g., less than 2 wt. % or less than 0.5 wt. %.

The finished ethanol composition produced by the embodiments of thepresent invention may be used in a variety of applications includingapplications as fuels, solvents, chemical feedstocks, pharmaceuticalproducts, cleansers, sanitizers, hydrogen transport or consumption. Infuel applications, the finished ethanol composition may be blended withgasoline for motor vehicles such as automobiles, boats and small pistonengine aircraft. In non-fuel applications, the finished ethanolcomposition may be used as a solvent for toiletry and cosmeticpreparations, detergents, disinfectants, coatings, inks, andpharmaceuticals. The finished ethanol composition may also be used as aprocessing solvent in manufacturing processes for medicinal products,food preparations, dyes, photochemicals and latex processing.

The finished ethanol composition may also be used as a chemicalfeedstock to make other chemicals such as vinegar, ethyl acrylate, ethylacetate, ethylene, glycol ethers, ethylamines, aldehydes, and higheralcohols, especially butanol. In the production of ethyl acetate, thefinished ethanol composition may be esterified with acetic acid. Inanother application, the finished ethanol composition may be dehydratedto produce ethylene. Any known dehydration catalyst, such as zeolitecatalysts or phosphotungstic acid catalysts, can be employed todehydrate ethanol, as described in copending U.S. Pub. Nos. 2010/0030002and 2010/0030001 and WO2010146332, the entire contents and disclosuresof which are hereby incorporated by reference.

In order that the invention disclosed herein may be more efficientlyunderstood, an example is provided below. It should be understood thatthese examples are for illustrative purposes only and is not to beconstrued as limiting the invention in any manner.

Examples

Examples 1 to 3 were prepared to show three different feed streams maybe fed to vaporizer 106. The acetic acid, ethyl acetate, acetaldehydeand diethyl acetal amounts were kept constant. The amount of water andethanol was varied.

TABLE 13 Example 1 Example 2 Example 3 Component Wt. % Wt. % Wt. %Acetic acid 62 62 62 Ethyl acetate 20 20 20 Ethanol 15 8 1 Water 1 8 15Acetaldehyde 1 1 1 Diethyl acetal 1 1 1

Each of the feed streams in Examples 1 to 3 were vaporized and fed toreactor 108. The acetic acid concentration and ethyl acetate conversionare reported in Table 14.

TABLE 14 1500 hr⁻¹ 2200 hr⁻¹ Acetic Acid Acetic Acid Ethyl AcetateConversion Ethyl Acetate Conversion Conversion (%) Conversion (%) (%)(%) Example 1 96.5 10.7 94.5 −7.2 Example 2 96.3 21.7 93.5 −2.2 Example3 95.7 29.3 93 3.1

While the invention has been described in detail, modifications withinthe spirit and scope of the invention will be readily apparent to thoseof skill in the art. In view of the foregoing discussion, relevantknowledge in the art and references discussed above in connection withthe Background and Detailed Description, the disclosures of which areall incorporated herein by reference. In addition, it should beunderstood that aspects of the invention and portions of variousembodiments and various features recited herein and/or in the appendedclaims may be combined or interchanged either in whole or in part. Inthe foregoing descriptions of the various embodiments, those embodimentswhich refer to another embodiment may be appropriately combined withother embodiments as will be appreciated by one of skill in the art.Furthermore, those of ordinary skill in the art will appreciate that theforegoing description is by way of example only, and is not intended tolimit the invention.

We claim:
 1. A process for producing ethanol, comprising: hydrogenatinga feed stream in a reactor in the presence of a catalyst to form a crudeethanol product; separating at least a portion of the crude ethanolproduct in two or more columns to produce ethanol and a liquid recyclestream comprising ethyl acetate, wherein the feed stream is produced bycombining an acetic acid stream and the liquid recycle stream;determining ethyl acetate concentration in the crude ethanol product;and adding at least 0.01 wt. % water to the feed stream for maintainingan ethyl acetate conversion of greater than 0%, when the ethyl acetateconcentration of the crude ethanol product is greater than the ethylacetate concentration of the feed stream.
 2. The process of claim 1,wherein the feed stream is vaporized in a vaporizer and wherein at least0.1 wt. % water is added to the vaporizer when the ethyl acetateconversion is negative.
 3. The process of claim 1, wherein the feedstream is vaporized in a vaporizer and wherein from 0.01 to 20 wt. %water is added to the vaporizer when the ethyl acetate conversion isnegative.
 4. The process of claim 1, wherein the catalyst comprises afirst metal selected from the group consisting of iron, cobalt, nickel,ruthenium, rhodium, palladium, osmium, iridium, platinum, titanium,chromium, rhenium, molybdenum, and tungsten; a second metal is selectedfrom the group consisting of molybdenum, tin, chromium, iron, cobalt,vanadium, tungsten, palladium, platinum, lanthanum, cerium, manganese,ruthenium, rhenium, gold, and nickel; and wherein the second metal isdifferent than the first metal.
 5. The process of claim 1, wherein thecatalyst is substantially free of copper, zinc, and oxides thereof. 6.The process of claim 1, wherein the liquid recycle stream furthercomprises ethanol, acetaldehyde or mixtures thereof.
 7. The process ofclaim 1, wherein a volumetric ratio of acetic acid stream to liquidrecycle stream is at least 1.5:1.
 8. The process of claim 1, wherein avolumetric ratio of acetic acid stream to liquid recycle stream is from1.5:1 to 20:1.
 9. The process of claim 1, where the conversion of ethylacetate after adding water to the vaporizer is at least 1%.
 10. Theprocess of claim 1, wherein the catalyst is substantially free ofcopper, zinc, and oxides thereof.
 11. The process of claim 1, whereinthe conversion of ethyl acetate is at least 15%.
 12. The process ofclaim 1, wherein the acetic acid is formed from methanol and carbonmonoxide, wherein each of the methanol, the carbon monoxide, andhydrogen for the hydrogenating step is derived from syngas, and whereinthe syngas is derived from a carbon source selected from the groupconsisting of natural gas, oil, petroleum, coal, biomass, andcombinations thereof.
 13. A process for producing ethanol, comprising:hydrogenating a feed stream in a reactor in the presence of a catalystto form a crude ethanol product; separating at least a portion of thecrude ethanol product in a first distillation column to yield a firstresidue comprising acetic acid and a first distillate comprisingethanol, ethyl acetate, and water; removing water from at least aportion of the first distillate to yield an ethanol mixture streamcomprising less than 10 wt. % water; separating a portion of the ethanolmixture stream in a second distillation column to yield a second residuecomprising ethanol and a second distillate comprising ethyl acetate,wherein the feed stream is produced by combining an acetic acid streamand a liquid recycle stream; determining ethyl acetate concentration inthe crude ethanol product; and adding at least 0.01 wt. % water to thefeed stream for maintaining an ethyl acetate conversion of greater than0%, when the ethyl acetate concentration of the crude ethanol product isgreater than the ethyl acetate concentration of the feed stream.
 14. Theprocess of claim 13, wherein the catalyst is substantially free ofcopper, zinc, and oxides thereof.
 15. The process of claim 13, whereinthe feed stream is vaporized in a vaporizer and wherein at least 0.1 wt.% water is added to the vaporizer when the ethyl acetate conversion isnegative.
 16. The process of claim 13, wherein the feed stream isvaporized in a vaporizer and wherein from 0.01 to 20 wt. % water isadded to the vaporizer when the ethyl acetate conversion is negative.17. A process for producing ethanol, comprising: hydrogenating a feedstream in a reactor in the presence of a catalyst to form a crudeethanol product; separating a portion of the crude ethanol product in afirst distillation column to yield a first distillate comprising ethylacetate and acetaldehyde, and a first residue comprising ethanol, aceticacid, water, or mixtures thereof; separating a portion of the firstresidue in a second distillation column to yield a second residuecomprising acetic acid and water and a second distillate comprisingethanol and ethyl acetate; separating a portion of the second distillatein a third distillation column to yield a third residue comprisingethanol and a third distillate comprising ethyl acetate, wherein thefeed stream is produced by combining an acetic acid stream and theliquid recycle stream; determining ethyl acetate concentration in thecrude ethanol product; and adding at least 0.01 wt. % water to the feedstream for maintaining an ethyl acetate conversion of greater than 0%,when the ethyl acetate concentration of the crude ethanol product isgreater than the ethyl acetate concentration of the feed stream.
 18. Theprocess of claim 17, further comprising removing water from at least aportion of the second distillate using a water removal unit selectedfrom the group consisting of adsorption unit, membrane, molecularsieves, extractive column distillation, and combinations thereof.
 19. Aprocess for producing ethanol, comprising: hydrogenating a feed streamin a reactor in the presence of a catalyst to form a crude ethanolproduct; separating at least a portion of the crude ethanol product intwo or more columns to produce ethanol and a liquid recycle streamcomprising ethyl acetate, wherein the feed stream is produced bycombining an acetic acid stream and the liquid recycle stream; andmaintaining a water concentration in the feed stream and maintaining aconstant ethyl acetate concentration in the reactor; provided that whenthere is net increase in the ethyl acetate from the feed stream, theprocess further comprises adding excess water to the feed stream tomaintain the constant ethyl acetate concentration.